I take it you do remove the paint on the surfaces that require glueing? This ensures that the parts stick to eachother and not the paint; makes for a much better bond. Also; this might prevent the glue from running and fogging up the paintjob.
Make sure the surfaces to be glued have been roughed up to increase the surface area and give the glue something to grab. I tend to score a fine grid pattern across those surfaces with an X-acto knife before glueing.
Oh; and don't use too much glue; when you feel you've put on enough, you've already used too much
