How can I play Asari Vanguard effectively?

It's my favorite character at the moment at Silver/Gold chalanges. I prefer it to the asari adept, since vanguard is much more versatile.

It's the best to play a supporting role. => Stasis is the most important power. Use stasis to defend your team against enemies. Phantoms for example. Biotic Charge is useful to jump from one point to the other to help your other teammates if they need help. Additionally use it to tank, to take hits, since you can repair your shields (Don't tank much on Gold however, when attacked by large crowds. Could be useful however, to save your squadmate). Grenades are extremely useful too if used right against big hordes of enemies. I throw all three grenades at once some times.

I prefer a shotgun Disciple, since it makes cooldowns really short (160% for Disciple I, gets better with each upgrade). Geth Plasma Shotgun worked well too. You could use a pistol instead, but it's pain in the ... to kill high-level enemies using pistols. Additionally it's good to use it after a Biotic Charge.

Overall, it's not the character that earns many points, but it's extremely helpful for the team.

I saw one Asari Vanguard top the charts on several of my silver matches in a row. I love my Asari Adept, and my favorite kill strategy is stasis bubble then headshots with my carnifex; it works better on standard mobs than spamming warp. This vanguard had the same strategy--stasis and headshots--but used the vanguard talents and a mattock, scoring better dps. He didn't use the charge hardly at all, and he demolished anything without armor.