What you do is use your cheap removals and efficiently trading minions early game to set up tempo for a strong mid-game where you deal major damage and have your opponent about dead or already dead by the time you enter late game.
Tempo rogue basically takes advantage of its low cost removals and good trading minions to stay ahead of their opponent through out the game, thus keeping tempo over your opponent. There are many ways to do this and understanding what to do, when to do it, and who to do it against can take lots of time and experience. Without a solid understanding of other classes it is very difficult to keep tempo if you can't even imagine what is coming.
Wanted to do a quick write up on play style since this plays so differently than the old tempo rogue. Rather than looking at just the single value of each minion you need to look at that plus the value of the deck as a whole. How does everything function together in order to give me the max value on each play to gain tempo over my opponent.
Deck plays like a combination of zoo and Tempo rogue, though it is not quick enough to be considered aggro, more like a faster mid-range deck. When faced with aggro and mid-range decks your going to be fighting for board control most of the game with them using minions and spells. Against control decks your going to take a zoo approach and flood and buff your board to the point that they can no longer control it and you just wipe them out.
Backstab- Staple Rogue card that should be used in every tempo rogue deck
Eviscerate - 2 mana for 4 damage, of course you will be running this card as a rogue
Deadly Poison - With your dagger you pay a total of 3 mana for 6 damage, cheaper then a fire ball.
Blade Flurry - Potentially the strongest AOE's in the game if you souped up your weapon enough. Though that is the best part about this card, it can be just as strong as you need it to be, buff it as you see fit then let loss on your opponents board. Whether your weapon a 3/1 for a zoolock board wipe or a 8/1 for a handlock board wipe. It can be what ever you need, and with all the board flooding happening right now along with the new weapon buffs, Blade flurry never looked better.
Tinker's Sharpsword Oil - A decent weapon buff, seen its best value when used with its combo. Though uncontrollable having an extra minion and weapon to trade up with against control decks like Handlock and Warrior this can priceless.
Sabotage - With Paladin being one of the top classes in the game right now having a hard removal combined with a weapon removal is always a great thing. Warrior and Hunter are also still around so removing one of there weapons can be awesome to. Rogue is very good at manipulating what is on the board so it is often very easy to get you target down to just the one minion you want to take out with this one. Also this works wonders on Handlock.
Cogmaster's Wrench- A great weapon, easily made into a 3/3 weapon at any time giving you 3 mana for 9 damage which is insane value right there.
Bloodmage Thalnos - One of the best cards in your deck, do not let his low cost, health and attack fool you, this guy is one of the most important cards in your deck whether you notice it or not. This card does 3 things in one Very nice card, it boost the spell damage on all your spells, and its low cost also gives you the ability to easily combo your other cards with it (great with eviscerate, blades flurry and even backstab or fan of knives), the card draw is the icing on the cake. Combo, Card draw and spell damage boost perfect card for a rogue deck.
Trade Prince Gallywix - One of the best editions to rogue in GvG if not the best addition. For tempo rogue it gives you a great weapon for fighting against control decks. If your opponent has to use a hard removal to get this guy off the board that is not a bad trade. Having an extra hard removal against a control deck can be the difference between a win and a loss. Even against aggro and mid-range this card can be great. It has a solid body for 1 and I cannot count how many times I have won games because of the spell my opponent gave me through Gallywix. The only efficient way to deal with him is through silence, and even silenced he is still a solid body. And if your lucky enough to have a Time Rewinder in your hand for that even better.
Loatheb - great at hindering your opponents tempo and also fills that 5 drop with a solid body that silencing does absolutely nothing to.
Iron Sensei - Great card, basically a 4/4 for 3 mana, and if your opponent fails to kill him on their next turn the value just keeps going up. This card allows rogue to play other mech's and get the value out of them that other classes cannot, like Target Dummy and Arcane Nullifier X-21. Just be careful, try to place him behind a taunt, and unless you absolutely have to do not play him on a board with no mechs. Without a mech on the board this card has no value, though in all honesty I have never had a problem with this personally.
Target Dummy - no other can take advantage of this card like rogue can. I have already talked about the value with Iron Sensei, this card is also useful for comboing. If you happen to be running Tinker's Sharpsword Oil, then even better. Though this card is great when you get it off, having to many of a good thing can be bad. I only run one, and I do not have trouble getting value off this card. Target Dummy's are best used in moderation. Still one of my favorite plays right now is turn 2 or 3 Target Dummy + Iron Sensei for a 2/4 taunt and a buffing 2/2 for only 3 mana, insane value. Also with the lack of taunt in this deck having an extra taunt can be the difference between winning and losing.
Jeeves - Works into the deck perfectly. Another great card made even better by Tinker's Sharpsword Oil and Iron Sensei, teaching mechs everywhere how to destroy. Taking advantage of your effectively trading minions can make it a lot easier on your card usage, but when your hand gets low, emptying it onto the board and following it up with this game mid-late game is a game breaker. Some people won't even remove him because they need the card draw as well, so at that point it is just a matter of who can take advantage of there cards the best, which tempo rogue just happens to be one of the best at in the game.
Piloted Shredder - Arguably the best card to come out of GvG, 4 mana for a 4/3 that spawns another minion after it dies. Yeah you can get screwed and end up with a useless card, but in the end having that extra card is still insane. God knows when you will be graced with Millhouse Manastorm.
Goblin Auto-Barber - A good mech, you never know when you will need some extra damage on your dagger. Just like some other cards mentioned, best used in moderation. It does require a weapon already up, so it is not a 2-drop, but still a great minion to trade up with and a buff to your weapon can really save the day.
Clockwork Gnome - Great card for a Tempo Mech rogue, it is the early board presence that you are looking for, and its low cost also gives it great combo synergy, combine that with the fact it also gives you a 1 mana spell when it dies, its combo synergy value just goes up. A solid card for a mech rogue.
Mechwarper - do I even have to explain? make your mechs cost less making it easier to use your combo cards efficiently. Auto include for deck
Annoy-o-Tron - Once again, a great card, made even better by Tinker's Sharpsword Oil and Iron Sensei, though best used with Iron Sensei. With all your low cost removals it is easy to make it very difficult to take this thing out on turn 2, even on turn 3 it can be difficult to deal with, This is the perfect card to play down right before an Iron Sensei, puts him behind a taunt for protection, while he buffs it up. The divine shield makes this card great for clearing minions to.
Harvest Golem - Harvest Golem offers unique utility and board presence that is necessary to help control the board. Against board flooding decks and Aggro decks he can be used to clear 2 minions. Harvest Golem will almost always result in a 2 for 1 card trade in your favor. Making more trades like this is what wins games.
Cards not used and why
SI:7 Agent - 2 reasons, 1 no mech syngergy, secondly the 3 drop spot is already crowded as is, that fact is the other cards currently in the 3 drop spot will give you more value in this deck than SI:7 card can.
Cogmaster, Tinkertown Technician - 1st off Iron Sensei is so good you do not want to many non-mechs in your deck and ruin his high value. Secondly the 1 and 3 drop spots are already filled up with minions, spells and weapons you can get higher value out of.
Spider Tank - 3 drop problem once again, to many 3 drops as is that are giving you better value than this card.
Micro Machine - So many 2 drops already that you going to get more value out of in more cases than you will with this guy. He is just not consistent enough for me. Yes great combo with the sensei, but already enough 2 drops and I think that Annoy-o-Tron and Target Dummy are better for the sensei anyways.
Piloted Sky Golem - Cost to much, just paying to much for the bad stats and a random 4 drop. The shredder cost just enough and gives you a minion good enough for his value, this one is just not there.
Assassin's Blade - enough weapon buffs as is, this card is just overkill at the moment.
Side Board and Card Replacements
Side Board (refers to cards that are good for use in this deck depending on the meta that you should have in mind)
My most often interchanged cards are a Tinker's Sharpsword Oil for Arcane Nullifier X-21. Arcane Nullifier X-21 is a card that can only get its true value in rogue. Iron Sensei and Tinker's Sharpsword Oil can turn this thing into a animal that only a silence or a Black knight can take out effectively. Though like target dummy this card is best used in moderation. When you get the value off it is an insane amount of value. Even so a taunt that cannot be the target of spells or abilities for later game can be very advantageous for you.
Trade Prince Gallywix really has no equal or similar card to choose from. if you do not have him, put another legendary like Loatheb or big body minion in his place.
Arcane Nullifier X-21 can be replaced with a mech or legend of your choosing.
Iron Sensei cannot be replaced, do not try running mech rogue until you have 2 of them.