Don't play anything but bot matches until you have a decent grasp of the mechanics, or you will be flamed, and it won't be fun.
Apart from that, start of with Strength heroes (preferably ones with at least one passive) Dragon Knight, Bristleback, Centaur Warrunner, until you know the skills of about 50% of the heroes (don't worry, that'll go quicker than it sounds).
Cont.
Apart from that, start of with Strength heroes (preferably ones with at least one passive) Dragon Knight, Bristleback, Centaur Warrunner, until you know the skills of about 50% of the heroes (don't worry, that'll go quicker than it sounds).
Cont.
No, just joking, didn't play myself, although I know how it looks.
Try picking ranged heroes at start, learn farming, don't greed for kills, farm more and buy items that are matching your character. Also try to play an easy one.
Also: teamwork.