Always use a very sharp knife. In my build thread I use one of them HK sells one very cheap as well. That blade lasts for a while and I made one whole plane with one blade and it didn´t loose sharpness.
Try to work as exact as you can to make the final product be looking and working nicely.
Start with a little bit more easy plans which describe in written text how and what to do. They help a lot with getting into the deeper skills of scratchbuilding.
Use good components. Scratchbuilding is also about choosing some good and reasonable componentes that fit to the weight and the thrust you want and don´t be dissapoint if the plane doesn´t go vertical. Start experimenting because that is what it is all about these days.
Don´t mess up any scales when drawing out the plan (rather print these days)
Use a long! and straigt! piece of wood or aluminium or whatever sothat you can run the blade of the knife along it sothat you a have a perfectly stright line of cut. (Metals are better because good knifes do cut into wood
)
Also practice you skills of cutting with the blade. You don´t believe how much you can do wrong but believe you can.
Also if you are unsure/not able to use a knife properly, just make a rough cut out and then try to get the actual line of cut by using sandpaper.
Puuh, that all from me from what came up into my mind
EDIT: Got some more
Use good glue! Some of the CA glues don´t work well. Actually I have one that etches away depron, which looks pretty cool but it is not the stuff you want. I personally use UHU Por but I´ve heard that you use some different stuff like Goop. Very important also the correct use of those glues.
TIP: If you glued something wrong, try to remove the glue by wishing it of with some benzin (some of that high concentrated stuff
) or other concentrated alcolhols or so.