1k mmr, 2k mmr, 3k mmr....the game play at different levels are really different.

Like how in 1k mmr, nearly no one buys dust or gems or sentry, so invi hero can really dominate the game easily. There's hardly any teamwork, so get a typical pub stomper hero & build, you're good to go.

In 3k mmr, you can expect sentry at the first few minutes already.

For starters, learn the basic dota mechanics first. Then master a hero instead of keep changing heroes every game.