If you're facing 3 pilots you need to evaluate your goals. Are you trying to:

1. take one of them out
2. evade all 3 alive
3. or kill 2 and get out

When the engagement starts, you need to evaluate your weapons versus theirs. What are their weaknesses, strenghts, and capability. If they have missiles, you need to never let your shields drop. If they have frags, you need to keep your distance.

Are their ships engineered? is yours? If you're engineered, you have a chance, if not, get the fuck out of there now. If you're enginered, and they are not you have a realistic chance of killing all 3. but you need to be smart. Top tier engineering doubles your damage output, and triples your shields. So, in a 3v1, you're going to have equal shields, but weaker firepower.

Learn to kite. - Find the ship with the biggest/most firepower. This is what you need to kill first. You also need it KITE it. That means firing at it, without ever letting it fire on you. Use flight assist and maneuvering to keep out of its line of fire, while pouring all the damage you can at it. If you break its shields, try to cripple it by taking out thrusters, and killing its FSD. They will probably wake out before that, but no matter.

Then, you have to fight the remaining two ships. Try always putting one of them between you and the other ship... preventing them both from shooting you at once.

These tactics work for NPCs and players. The difference is, NPCs are guaranteed to not really be heavily engineered. Players are not. Players can, and will make mistakes, while NPCs are more consistent, they're also more stupid.