^^^Bad Advice^^^ lol
I hate telling people how to get free.

IF YOU GET CONQUERED BY "SPYDA" JUST LOG ON ONCE A WEEK TO KEEP FROM BEING DELETED....
If you're conquered by anyone else however....
Building a substantial army is usually a decent way to go. If you try to rebel without one you will undoubtedly fail. And even if your conqueror is too busy or doesn't notice and you get free. You'll be attacked and conquered again before you can even log in the next time.
Personally, I've found there are 3 ways to really get free...
Strength, Relationships, or Running.
You can either take an approach to wait it out, get strong, and hope you survive long enough to meet a decent alliance to help protect you.
You can build a relationship with your conqueror (Unless they're a jerk) and many times they'll show you the ropes on how to improve and have more fun, Or you can build a relationship with other players and try to start/JOIN (better option) an alliance. *DON'T ask a top alliance if you can join unless you have some serious achievements, as they'll likely turn you down straight away (if they bother to respond). Look for middle of the road alliances NEAR YOU and ask them about openings* Remember there's safety in numbers.
Lastly you can build an OP somewhere else and relocate. Many times this will get you free easily. However you'll have virtually no army at your new location and may be a sitting duck. Or you may walk into an even worse situation.
ABOVE ALL ELSE. DON'T, DO NOT, AVOID, IF YOU EVER WANT TO GET FREE STOP YOURSELF FROM...
Spying, Constantly spamming, ion cannoning, spam messaging, and anything else you can think of doing to just annoy your conqueror. This just makes them mad and remember your name. I once had a conquer who Ion cannoned me every...single...day.
I relocated near him then moved him in the middle of my alliances nuke field.... and I sent him this msg. "Try to Ion the 10 nukes coming at you." in the end, his colony went inactive and was eventually deleted. But I got over a week of peace and taxes to recoup my losses.
It's usually not a good thing when people really don't like you.... It's always a bad thing when they're stronger than you.
Getting unconquered is easy. A couple dozen units and a fully charged shield can take care of that. But STAYING unconquered.... That's a different matter, and one you won't be able to pull off alone in most cases.