try and be a bit more specific. it might be an idea to get stuck into a game and then post your questions as you play......i'm only in my second game, and i ran into a few problems and got plenty of advice here.....some very hepful people around.
as for civs, just go with what you feel like, as a beginner i don't think it will make too much difference.
In my opinion, there is NO reason that you should ever sell techs to the AI. There are many reasons for this...
1. Early on in the game, you'll only be able to get money (and just a small amount of it) for your techs. And until you advance to another form of government (not despotism), the money does little good. You cannot pay for quick production of troops, just increase spending in science or luxury.
2. When you sell a tech to another civ, they almost immediately sell it to everyone else. Your scientific advantage goes down the tubes.
3. It can allow the AI to research mapmaking earlier in the game, thus giving them an expansion advantage that you can do without.
---Try the other way around. I stockpile $ as a despot for 2 reasons. To buy tech from others, and later to buy their maps.