1) Apply base makeup in this order: color correctors, foundation, concealer
2) Conceal dark circles by doubling up on your concealer - put concealer under your eyes before applying foundation and after.
3) Prevent your foundation from breaking down/ cracking by applying primer on your T-zone to make oily skin matte
4) Based on the coverage you need choose between a sheer, medium and full coverage
7) If you have oily skin, use an oil-free foundation formula to avoid breaking out. The heavier the formula the more prone to clogging your pores and creating breakouts. It is better for everyone in general to use a water-based formula to avoid the above.
8) Choose foundation based on your undertones: warm, cool, neutral. To understand your undertones its simple: if you look good in gold jewelery you have warm undertones, if you look better in silver you have cool and for both you are netral. Another way is looking at your veins, if your veins are green: you are warm if they are greyish you are cool. You can also try it with clothes - if white washes you out you are cool if it enhances you, you are warm.
9) If you want a subtle glow mix an illuminating formula in your foundation - a pea size drop is enough on the back of your hand and a quarter-size of foundation - blend and apply to areas you want to glow: basically natural highlighter. For a more dewy finish you can apply facial oil onto a sponge and blend your foundation using that.
10) Color correcting is key to not buying two shades of foundation (winter & summer). Alter the shade by adding a couple color-adjusting drops. Use the color correcting guide to adjust the shade so it is not too dark or too light.