Hearthpwn

Playing this deck is pretty straight forward, you fight and maintain board control until you can simply out-value your opponent with cards like Spiteful Summoner which will give your opponent a bit of an headache and a real hard time dealing with.

Overall I'd say it's a rather simple and easy deck to play since it's pretty curve-oriented most of the turns. However there are exceptions to this rule which can present you with some really hard decision making, especially in the later stages of the game in which you start getting different type of plays you can do with cards like Splintergraft & [card]Zola the Gorgon/card].

You should also be careful by not overplaying your hand. The cards in this deck are rather sticky so if you playing versus someone with mass-removal potential you rather want them to be forced to use it on fewer of your minions or make them feel like they need to trade with weapon/minions instead and since you are a druid your minions are sticky so once you have that board advantage it's very hard for your opponent to do much if you find that sweet spot in which he can't out trade you and lose by using up all his resources due to you being able to follow it up with just more nasty hard to remove targets.

Vs everything: You always keep Prince Keleseth & Greedy Sprite and you never keep Ultimate Infestation

Don't be afraid to hard mulligan if you don't get either of the "always keep card" above along with a bunch of cards that don't really do you any good vs the class you're facing. 

Fire Fly is also good versus pretty much everything so there's really no reason to throw that away either however it's not as important as the ones mentioned above. This deck is very tech oriented so if you come across a paladin you can keep a card like Mind Control Tech and versus a warlock you could keep a Spellbreaker given that you have some cards you can get out on the board before that.

So the composition (curve) is the main thing you should keep an eye on other than the high priority cards, after that you have the tech cards. versus aggro you early board is important which makes cards like Druid of the Scythe very important while versus slower decks you can keep your Spiteful Summoner around (if you have a good early hand like a Fire Fly + Greedy Sprite you could probably keep the summoner against everything). 

Harrison Jones is also a card you can keep if you know your opponent have a weapon and your hand can support keeping a him around. Another card worth mentioning in this context is Glacial Shard since it's a 1-drop, yet it isn't. You don't play this card on turn 1, you keep it around until you can get value out of it by getting a minion out and deny your opponent the ability to remove it with one of his, it's also a very efficient synergizer with harrison since you can lock down a weapon for additional card draws with harrison the turn after. 

Zola the Gorgon & Splintergraft is in this deck since they synergize very well later into the game. I'd only keep zola if I also got Prince Keleseth in my starting hand since most people don't trade/remove the prince unless your a rogue, if you are able to get out that combo you can't really lose due to you having 28 minions in the deck and the pure value 2x prince adds to that.
However you will have minions on the board most of the time mid-late game, sometimes very big ones like lich king will survive. The main target to copy is obviously the spiteful but if you need another tech card like a silence don't be afraid of copying a spellbreaker or an additional big card like lich king, go for it... When you have 1-2 smaller minions with 1 big one as a druid and can keep that board up while simply trading away with your opponents minions he will run out of removals due rather fast while you can keep the momentum going and go in for the kill.

I could keep on going but it would just become a big wall of text so tl;dr, use common sense. Look for early curve/high priority cards and what's good against the class your facing.

You can fast forward 10 minutes or so since the "starting soon" got rather long due to me spilling juice all over myself. Then I make the deck for 15-20 minutes, I obviously talk some about my choices and reflect on the cards (I think, I was tired). From min 30 and forward the gameplay starts until the end of the stream. Parts of the stream is muted by twitch due to copyrighted music in the background but there's an hour or two with me commenting on my play.

In total, 71% (12-5, starting from rank 5 no stars). The high % is probably a combination of me playing good, the deck being solid and a bit of luck. I wouldn't read too much into it since it requires about 50-100 game in order to see a more accurate stats and patterns. I grayed out the names due to respect of privacy.