I'm wondering how to successfully glue painted parts together withouth damaging the paint? Sometimes you just have to paint a part before glueing it in place, like parts in interiors or engines and such. Or when glueing painted cockpit into the painted fuselage. Any tips?

When glueing painted parts the best thing to do is to gently scrape away the paint from the areas where the two parts join. Then apply the glue carefully to these areas so that it doesn't touch the paint.

I agree wholeheartedly with brandydoguk, whenever its possible,
youll be pleased with the results it yeilds, also think to scrape the innards of a hole that is made for a piece to fit into like a head lamp poet, etc
If you cant, be sure to use a clear fast drying cyano

I use either fine sandpaper or sandpaper twigs before gluing.

I used to wait until the whole tank was built before painting but it became kind of tedious.