The different "stages" of "normal" spaceplane ascent go as following (assuming rapiers or rapiers + nukes):
1. Subsonic stage. Get the speed above 400m/s. The point is to get to supersonic speeds where rapiers start working properly and producing significantly more thrust. If your plane doesn't have huge amounts of (unnecessary) thrust you probably have to go pretty much horizontal here and not try to gather altitude yet.
2. After you have sufficient speed (~400-450m/s) you start the climbing stage where you slowly pull the nose up and fly up to thinner atmosphere to minimize drag. The ascent angle here is very craft dependent but can be something like 10-20 degrees.
3. Acceleration stage. Once in the thinner atmosphere you start to lower your ascent angle to keep in the region where jet engines still work to gather as much speed as possible using airbreathing jets. You should be flying almost level flight (just slightly ascending slowly) at around 20-23km here and try to get speed as high as possible before switching to rockets.
4. Rockets and/or nukes stage. Once you stop accelerating with jets it is time to switch rapiers to rocket mode (if I'm using nukes I usually fire them up a little earlier and then switch rapiers to rocket mode after they flame out completely). Depending on TWR and your initial ascent you probably have to burn little over the prograde marker on the navball at first and then lower the nose to prograde when time is right, Also this is the stage where you will have to watch the overheating issues. Just keep burning (as close to prograde as you can without blowing up) until your Ap is out of atmosphere. If executed correctly your Pe should also already be pretty close to appearing above kerbins surface once your Ap reaches 70+km.
5. Circularization stage. Obvious and easy. Keep pointing prograde. Coast to apoapsis and circularize.
