Ok, here's a rough guide:
General rules: When attacking a turret, keep jumping around it. So, take a swipe, then jump on the other side of it, and take another swipe. This way the turret is spending far more time turning than shooting, and a good player can single-handedly take down 2 or 3 turrets as a Basi with this method. But don't attempt anything crazy, always run away as soon as your hp gets down to around 50%. Also, learn what structures to destroy first: normally you want the armoury or medipad down, then go for the reactor or telenodes. But, if you see a good opportunity to take down the reactor, or all the telenodes (has to be all), then go for it.
Dretch: DON'T. Go kill some easy prey, or build, until you've got at least 1 but preferably 2 or 3 EP.
Basi/Adv Basi: You don't have the hp to survive long against turrets. If there are 3 or less turrets you can run in, take a couple swipes at one, escape, and repeat.
Marauder: The first alien who can do decent damage to a base. Basically, bounce sporatically around the room chomping things, preferably focusing your chomping on a specific building. But remember that as a marauder, boucing around the room at all times is more important than making every slash count, so never stop hopping around. The mara is very good for the turret-killing technique mentioned in General Rules.
Adv Marauder: Good for taking out turret clusters or cramped bases. Against clumps of turrets, use the turret-killing technique while zapping the turrets instead of slashing them. The chain lightning can take down large amounts of turrets. Use same technique for clustered buildings. Zapping the same structure several times will kill it faster, so if you're focusing on, say, the armoury, always aim your zap towards it. (zap damage decreases after every segment)
Dragoon: Heavy damage, but big hitbox. Pounce in, chomp things, pounce out. And try not to get too much turret fire, since you do have a fairly large hitbox and aren't as agile as a marauder.
Personally, I find marauders and adv maras are the best for taking out a base, pre-s3. However goons have more power and are more suitable once the turrets are gone.
Random attack strat: It's effective to have a double-alien combo when attacking a cluster of turrets. The first alien runs in and leaps over the turrets and runs out of range of them (proceeding to attack any defenders there). Then the second one goes in to attack the turrets, which are now all facing backwards. If the first alien isn't occupied with defenders, this can be repeated over and over.