I would suggest, when doing a skin, that you complete all the panel lines first. Do these with light grey or white solid colors covering the entirety of the plane's wings and fuselage (etc) so that you can see where there are problems.
Then I would strongly suggest you do BOTH sides of the plane at the same time. Don't just do the left side wing and fuselage, because then when you go to line the two up you're backpedalling quite a bit to get it to look as a single continuous pattern.