As Mumblefratz already said, can you give some more pointers as to what's going wrong? I mean, why do you lose to the AI's, are you being outresearched, outcolonized, is their military too strong or to they attack you too early, etc?
Below I've already added some tips...
1) Try to get some technologies with an econ, morale, production bonus from the AI, purely by trading away influence points or technologies that they won't benefit much from (e.g. sell them "beam weapon research" if they've got far more advanced missile technologies researched)
2) When setting your taxes in function of approval, check the list of your planets: it's not necessary to have 100% or 76% average approval since the population growth is determined per planet. Having 76% or 100% approval on an individual planet gives you a population growth boost on that planet.
I often find that I get a lot more income (or rather, less negative income) by having a few planets below such an approval threshold, as long as the majority of my planets still gets a population growth bonus.
3) Trade ships. I really depend on those early on to keep my economy afloat. While it's not best practice and more experienced players will find way to avoid this, I find that it helps if you need the additional income. In addition it improves your relations with the AI, so choose wisely with whom you want to trade.
4) A mistake I often made, was to go for the most distant planets I could grab (at least in medium or large galaxies), in an attempt to get a big span of control early on. In fact, it's better to choose your first few planets to colonize closer to your home planet: the sooner your colonies are up and running, the sooner you can have them produce more ships.
5) Keep an eye on the military graph (the default view shows population); as soon as the AI starts having any military, I typically try to follow that evolution, to avoid that they see me as the weakest prey. Of course, that's the bare minimum you should do; if you're able to pull it off (at first, try this at lower difficulty levels), try being the race one with the biggest military rating.
6) Hull size and weapons! Unless you research miniaturization and weapon technologies to advanced levels, try beating the AI to medium or large hulls. This is again to get your military rating up ánd to have stronger, better armed ships if it comes to combat.
7) See if you can bribe one AI into attacking another. If they're busy fighting, there's less chances of them attacking you...
8) Galactic resources: apart from building colony ships early on, also build some constructors to get your hand on these valuable resources which will give you a bonus to economy, research, military, morale, influence. Don't underestimate the effect of a well-developed galactic resource!