Legend more than anything is about the grind. Sure you need to play a good deck and know how to play it well against all your matchups, but the difference between legend and high diamond is you have to play a lot of games. I saw someone said that they auto concede their bad matchups. I usually give it a couple of turns to see if I have a chance against my bad matchups. I agree though that you have to just accept that you will lose some matches and move on. I have also seen it said to not focus on your rank just play for wins. That is also good advise.
I first got legend about a year ago. Was not working and had the time to spend playing a couple hours a day for the month. I took Galakrond Rogue to diamond 2, but then hit a wall. I kept fighting between rank 4-2. Towards the end of the month every time I started winning I was met with non stop aggro demon hunters. No matter how I changed the deck I still had a bad matchup, and changing the deck made other matchups worse. I finally switched to Big Dragon Druid and got there. My point being that it is good to stick with a deck, but sometimes if you are facing a specific meta you might want to change the deck at that time.
Overall though just be prepared to play a lot of games and don't let losses bother you. That first time I reached legend was on the last day of the month with only a couple hours left.