The best way: Spend as much time as you can practicing together. As a new team just playin 5 man-stacks in matchmaking is good practice. Pick semi-serious lanes (dont have to pick the most imba heroes/lineups), but pick roles and lanes that you would normally sort of use.

Try your best to find teams to scrim with: #dota2.cw on irc is the most active place right now. Build contacts up with other teams you vs, to try arrange scrims, learn about where the community operate on Irc/forums to try find connections/scrims.

Finally, participate in any and every tournament you can. As a new team in the beta that isn't easy, but there are a couple Open-tournaments. The best by far is the JeeLounge/Jeesports (whatever their site is called) Dota tournament. Their first Cup is already started, but the qualifiers are already running for their second Cup. You can read more about it on their site. It's not a big prizepool but there is some, and you will find some top teams participating in this tournament.

Additionally, there are various open tournaments with no prizes (just recognition) or very small prizes (excello cup giving mousepads or something) which are still worth playing for the practice.

Our team, Absolute Legends, played in everything we could when we started going competitive, it wasn't about the prize money or even vsing the best teams to prove ourselves, it was about the practice. Practice so we could get better and improve.