Well this was something new to me that I had never done until my last model a 1/72 P40 Warhawk...
Here's my secret:
I hand painted mine, and havent tried airbrushing them yet.....now on to my method.
1) Pull the canopy out....
2) Run in the kitchen grab a favorite bottle of whatever Alcohol you drink....
3) Pour a drink, come back to the bench and sit down....
4) Look at the cockpit and take a nice long sip....
5) Pick up the cockpit and take another drink...
6) Set the cockpit back down and you got it take another drink....
Repeat the above steps until you have a nicely finished bottle of crown(or whatever you prefer)....and still have a clear canopy!
Sorry I couldnt help myself, I dont have any secrets.....I did find that if I was getting frustrated the best thing I could do was set everything down and walk away.....I think I was away more than I was working. Thank God for these forums!