Some tips I've picked up over the years....
1: You can use a toothpick to paint small detail areas such as gauge clusters, white lettering on tires, windshield wipers etc...
2: Use Sandpaper on the tread of tires to make them appear to be used.
3: Use Future Floor Wax to cover decals and make them appear to be painted on. Just paint it on with a brush, its self leveling so no brush strokes will be seen.
The floor wax can also be used on the plastic windsheilds to give them the glass look and not the distorted plastic look.
4: Prime everything you are going to paint!!! In doing this there is less chance of the final paint seperating on the plastic part. I wash all the parts of the kit in dawn dish soap then blow dry on low. Then I prime it all before cutting the parts out. Once I detach the parts from the mold and shave the little nubs off, I touch them up with primer.
5: You can use old wire from electronics for sparkplug wire instead of buying the ridiculously priced detail kits.
6: Buy a pin vise...you will need it for detailed work.
7: Use salt to get a paint chipped effect on leading edges of wings on aircraft or any other thing you want to be chipped. After the part you want to be chipped is primed, mist with water, sprinkle salt on the area you want to be chipped, apply final coat of paint, knock off the salt and you will have a paint chipped look.
8: I use chalk, browns, black, gray, white for areas that I want to look dirty.
Just sand the end of the chalk on sandpaper and dab a qtip or brush in the powder, then apply to the areas you want to look dirty.
You can also use graphite powder for road grime. It sticks really well but dont use too much or it will appear shiny and not grimy. I add black chalk powder to dull it up.
There are tons more and I will add to this list when they come to mind.
If anybody knows how to use the metalizer paint for models let me know...I have no idea how or where to begin. I'm affraid of botching a model up. This is the reason a P51 I've had for a while is still not complete haha!