Easy Champ Picks:
Bruisers(Easiest to play);
Garen, Riven, KhaZix, Jax, Darius(most OP) and maybe Lee (can't use wards to jump)
Cho, Singed, and Malp
Lux, Ryze, and Kennen
Good early games usually wins a game(as long as you take advantage of mid game). Focus on early game items. Tear of Goddess is a good example of what not to get in most situations. Dorans can easily be abused to win in 3's especially on people like Garen.
Even though new three's has more objectives and team fights that take you away from lane, remember to focus on farming because a good cs regardless of altars will still win you games.
Because of map layout and objectives losing a tower is more devastating, use this to your advantage and push t1 tower as soon as possible.
And as always use your minimap as much as your normal screen. Never depend on your teammates for mia calls.