As always, I would not recommend actively choosing a single champion to "main," but rather let circumstance and preference in individual games dictate who you play most often, so you wind up playing the most of the champions who you find to be the most useful and fun to play. If what you are after is simply mastery of a given champion, it makes perfect sense to play that champion almost exclusively in a long series of blind pick games, so long as you do spend enough time with other champions to be flexible if your champ is banned or countered.
I mostly play bot lane, so I'm not in a terribly good position to give advice on proper top laning (my top laner of choice is Urgot, and I am terrible with melee top laners). Even so, I would advise you to work hard on two things after you have your champion mechanics down: Unless you need early kill potential for snowballing (Riven and friends), take teleport and practice using it to gank/counter-gank and participate in major fights. Doing so will instill the fear of GOD JAX in your enemies, and can turn the tide of an otherwise even game, so long as your sudden departure from top lane does not create a problem of its own. The other advice I give to players of all roles: Ward furiously! Any time you have enough gold for a ward, buy one and place it. If possible, maintain a pink ward near an important route. Upgrade or replace your trinket once you reach level nine, and continue to use it furiously. Top lane may seem like an island, but it is very important to work for the entire team, even if it feels like a solo game against your lane opponent. By spreading vision control on the top side of the map (especially the enemy jungle) and teleporting to major fights, you can transform your puny little island nation into a full blown British Empire.
, Jax 
, and darius 
. I'm open to using other champions though. (also please include tips for top laning :^) )
, never leave lane
Picked him up at first fed like crazy now I dominate every match up except 