Well, that's kind of vague, how exactly are you getting beaten? Tech or military or what? Anyway, here are some tips:

1) Play on a difficulty below "tough" which is he fair difficulty level.
2) Expand quickly at the beginning of the game. Buy some factories on you homeworld, then switch 100% spending to military to build colony ships quickly. Try to get more planets than each AI.
3) Next, build the basic factories, labs, and lots of markets on your planets. That will get your income, production, and research going for a strong start.
4) Trade techs with the AIs often.
5) Decide on a strategy and then focus on it. Military: research weapons, defense, hulls, engines, miniaturization, logistics, and invasion techs, build lots of ships, and invade planets. Diplomacy: research diplomacy techs, bribe friends and make them allies, then help your allies destroy civs that won't ally with you. Influence: research the influence techs, then build influence starbases near enemy planets to flip them to your control. Tech: defend yourself and research.
6) Ask more questions on the forums