Normally your opponents are all beatable, only stage 12 should give you problems.
Depending on what ninjas you have to work with, get a lineup with an acu in it (hinata is your basic ninja that does this, and also good since she can tank r1)
Learn how to position your ninjas, the enemy AI will always behave the same in terms of reactive or active skilling. Keep interrupting the ninja thats about to skill by using a faster position ninja and you should be able to beat them without suffering damage.
Some tactics I used when f2p:
1) Tsunade is a good target to draw attacks (especially those r1 tobi hits) if your battles generally go to round 3.
2) A r1 initiator is good to proc chases since you know exactly how their position is (naruto, kank gnw).
3) Having an acu is not always needed against enemy barrier ninjas, sometimes its prefarable since the barrier ninja will always be used by AI to skill in the next round, easy chase acu target.

Survival pretty much teaches you how to optimize placement and initiation.