it is recommended that you play against bots, even if you have a lot of experience playing war3 dota and/or games such as LoL and HoN.

for one reason, GRAPHICS/SOUNDS to get used to. for another, it's just a downright big game, meaning lots of items and heroes to learn. you also need to learn about how gold and experience gain and loss works, and strategies, and teamwork.

you will ruin many decent players' gaming experiences if you jump in too soon.

i would recommend learning how to DOMINATE the enemy bots throughout the game, from start to finish, with at least 3-5 heroes from each attribute type, agility, strength, and intelligence, before venturing into matchmaking. iow, learn about 9-15 heroes, a nice variety of them, and learn them very well, before stumbling along in matchmaking and potentially pissing your allies and enemies off.

you should also try every hero in the game out to see what they are like and figure as best you can what their strengths and weaknesses are so that even if you don't like them, you know how to deal with those heroes when the enemies pick them, and so you know how to work with those heroes when they are picked by your allies.

i can't stress it enough, dota 2 needs people to learn their place. you might be a very humble person since you're here looking for advice, but a lot of players don't look for advice and aren't humble, they might think they're hot stuff and jump into matchmaking way before they're ready, thinking 'everything will be okay'. well, it won't.

games are easily lost by hero picks alone, and if for example you merely only can play well 1 str hero, 1 agility hero, and 1 intelligence hero, what if your team wants a str hero and someone already picked your hero? or worse, what if all your picks were already taken? so you see, being flexible is pretty important, and hero roles aren't only dictated by str/agi/int, that was just an over-simplified example. at best you'll pick a str hero you're poor with or know nothing about, and stumble your ally over and over as you try all game to learn the hero and get it right. at worst you'll pick a hero your team doesn't need and you'll be redundant, getting picked off around the same time as your ally, or you'll be competing for the same kills and allowing other heroes that neither of you can kill to escape or dominate time and time again.

then there's strategy, and that is a whole other matter entirely. if you're a new player you're hardly qualified to debate strategy with your allies or even offer up strategy when no one has any ideas when your team is trying to figure out how to win. how can you know for example that you must keep on the move to avoid getting killed by tiny's dagger+avalanche+toss combination? or how can you know that you need to buy wards to keep on eye on what your enemies are doing when they are wandering around and/or stalking you or your allies?

well, you should be learning all these items and using them all, too. that goes along with learning the heroes. you don't have to be great with all the heroes and all the items, but you should at least develop your knowledge so you know what is what. you should be able to know the difference between for example, a shadow blade and a blink dagger, and the difference between a maelstrom and a cranium basher. and you should likewise know the difference between a null talisman and a bracer. and so on and so forth. you can't strategize much of anything if you don't know what it is in the game you are looking at. and what is worse, you have a hard time executing strategies suggested or demanded by your allies if you are unfamiliar with components of that strategy(for example how to use a certain item or hero skill, how to fight against a certain enemy hero or item).

so, LEARN dota 2 before jumping into matchmaking, and IF YOU DISREGARD this or not, at the very least WARN your allies that you need help learning the game AT THE START OF EVERY MATCH.