I've been flying a twin (C303) for six years now. SE performance with any real payload on take off will always be marginal. Good rule of thumb is max weight of aircraft in lbs divided by 20 will give you the minimum power required to keep it in the air, assuming you do your drills well (thats another question).
So with my aircraft max weight is 5250lbs and I have 250hp a side, so if I am full weight I know that I am not going anywhere in a hurry after EFATO. Likewise if the gear is down, or more than 10deg flap, and I haven't accelerated to VSSE, I am probably not going anywhere. Pre take off brief yourself and stick to it, know when your aircraft will fly on one and when it will not and be honest with yourself. If one gives up the ghost at a performance critical moment, retard the other and treat as for a single engine aircraft. If weight is good you have accelerated and are relatively clean, continue. For heavens sake, though, don't hang on to a bad position hoping that the laws of physics will miraculously change in your favour.
The benefit of the twin is really for long trips over water or hostile terrain, night and IMC flights, where if you are in cruise and stable, an average amount of skill and practice should still see you able to land the aircraft at a civilised location of your choice if you lose a motor
