Just some things I've picked up;
Take care of your skin, moisturisers and primers make a huge difference. Make sure to remove all of your make up before going to bed, and cleaning your skin and applicators before putting make up on again.
Apply foundation in a downwards motion, and avoid products with a glitter or shimmer affect so it doesn't accentuate your pores or wrinkles.
When it comes to make up, you usually get what you pay for.
Eyebrow shape makes a big difference.
The right shade of foundation should "disappear" when applied to your cheek.
Q-tips are good for applying eye shadow and correcting mistakes.
Do not pump your mascara wand, as it makes it dry out faster. If it smells "mouldy" throw it out.
Hold the mascara wand vertically to apply it to your lower lashes.
To avoid clumps let the first layer of mascara to dry before applying another.
When applying false eyelashes, cut to length and apply a thin layer of glue, wait 20 seconds for it to go "sticky" and carefully apply as close to your lash line as possible, keeping your eyes closes for a few minutes. Use mascara to blend it with your natural lashes.
I may think of some more later (: