I'm a quite new GalCiv2 player, but literally lived a whole year and six months in Master of Orion 2. (pretty much and older GalCiv from a different company). I play on a giantic galaxy with max number of opponents, by the way. It's the only way.
* First, research something to help your planet. This helps you in the long run.
* Second, squeeze out a few custom colony ships to get the civilization up in size. Although the individual planets won't make much money, they will all contribute quite a bit combine. Plus, if one planet makes -20 and the other +30, that's +10 overral. Consider it. (completely random numbers, by the way.) And when I say "custom" ships, it's because it gets you comfortable with the editor, and I can't be the only one who prefer to have "my" ships instead of the standard, boring ones.
* Third, create a custom scout design and keep sending them on auto explore. Don't worry, you can just scrap the ones you don't need later on.
* This path will quickly give you a decent sized empire, and sooner than later, you will run into other races. I suggest making friends first, as it's important to know your enemy. First be friends and get to know the other race, then nuke him back to the stone age.

* Found a second race? Good, good. That makes things more interesting. Make friends with both, have them, *ahem* protect you against your enemy and watch them blow each other up. Then, nuke the survivor back to the stone age unless he surrender. Alliances are great for this. If you are in an alliance with one, he will try to protect you.
And that's really all there is too it.

Hehe, nah, it's more complicated than that. But that's just one way to certain victory. Unless they don't fall for it, of course. In which case you should just get a big fleet and try to crush them before they crush you. That's always a possibility.
And as for the tech tree, didn't you get one in the box? I have a big poster-thingy with all the technologies right here. There is also a great tech tree in the game in the research screen. Just press and hold the left mouse button on the tech tree and drag the mouse. It takes a while, but you can see the entire tech tree here. (I'm using the 1.40x patch, though I think it is in the original game if anyone still have it.)