Hearthpwn

Midrange hunter is a fairly easy class to play. Just follow these steps:

1. Developing creatures to the board is the way you win with this deck. Try to have clean plays for every turn that use all mana effectively
2. Try to play around some cards such as rogues Sap which can be a huge tempo swing f.ex. with Highmane. Or, don't puke your whole hand to the board when you could guess enemy has AoE clears and so on. You get it and you get better recognizing these factors with experience
3. Try to use all your mana. Using your hero power is very often an effective way to do this. 
4. Hunter has the ability to keep the game fairly even for multiple turns and suddenly end it with cards like Kill Command(s) + Hero Power + Weapon + Quick Shot + All creatures face and well, whatever you got. Try to surprise your opponent if possible so they don't have time to heal.
5. Hunters don't heal. Unless you want to include some healing into this deck, be careful while face tanking. Especially on the later turns you die fairly easily if <15 hp. Develop creatures, control the board, win the game.

Try to get a one-drop. Even though this is obvious, it's especially important when your deck is based on developing creatures and controlling the board. You usually shouldn't keep big drops since you need to use your mana efficiently in order to win the game. Try to have a good curve, but also consider who your playing against. If you're against Shaman with a Quick Shot, you may want to keep it. One again, experience.

Check here: http://www.hearthpwn.com/decks/566135-s27-legend-midrange-with-a-guide On some parts that may be outdated (not too much though) and it doesn't include all new decks but you get the idea. And you know what also helps? Experience. I can't stress this enough. This is the only thing you won't get from these guides.

You see we have multiple beasts in the deck. That is supposed to work with Scavenging Hyena and you have a chance to build it to be huge. Works also very well with Unleash The Hounds. (Some time back I played this deck with 2 x Knife Juggler and 2 x UTH. If you want it, you could try. Haven't tried myself right now, but could still work.)

Beast synergy is also very important with Houndmaster. The fastest wins many times include a turn three Grub and turn 4 Houndmaster. Try to use this effectively especially for trades.

Barnes is a very good card for this deck: Eveything that has a deathrattle works with barnes. The strongest ones are of course Kindly Grandmother, Wolf, Hyena and the sickest of them all, a turn 4 1/1 Ragnaros.