Some tips on products, both in general and some more specific product/brand-based tips...
...in no particular order, but roughly added into sections.
These were just stream-of-conciousness tips; I may do another of these posts in the future as more tips occur to me!
Apply cream/gel blush after your highlighter (especially if you are using powder or loose pigments as a highlighter), otherwise the pigments will stick to it and you'll get a concentration of colour that's hard to blend.
Mix a cream blush together with an illuminator (like MAC Strobe Cream or any other) to give a very photo-friendly high shine cheek colour.
For oilier skin types, Make Up For Ever Uplight is a great gel-based highlighter that will set even on oilier skins, when a powder highlighter is not desired.
Apply a little moisturiser to your foundation brush to avoid soaking up too much foundation in the brush.
I've found sable brushes to be by far the best for eyeshadow blending.
Base: Foundations / Concealers
Use your fingers to apply Nars Sheer Glow foundation.
Avoid products with titanium dioxide for foundation but especially for under-eye concealer as this causes flashback in flash photography.
Your foundation brush is the best eraser/blender you have. Use just whatever foundation is left on it to blend over and out your blusher/bronzer/contour if you've added too much... or to shape your eye makeup up and out if you need to.
Use an eyeshadow primer and a corrector/concealer under your eyes, warm the products into your skin by gently pressing with your fingers, then blot away the excess oil with a 1-ply tissue, before then cementing your under-eye concealer work into place using a dusting of powder - this will prevent your under-eye concealer from creasing.
When I use MAC Studio Fix Fluid, I always make sure to moisturise extremely well first, then I buff it in with a MAC 109 - this gives a lovely flawless finish to what can otherwise be an uninteresting foundation.
Blotting papers are expensive, instead, head into a salon services shop and buy a bunch of the endpapers that hair stylists use for perms. The same thing, but much cheaper.
Before you use a setting spray to set your liquid foundation, make sure that you set with a powder first.
MAC Mineralise Skin Finish, buffed into your face with a kabuki brush, and finished off with a spritz or two of MAC Fix+, makes for a very fast and beautiful natural finish, medium coverage base.
Apply a sapphire-blue eye pencil along the waterline instead of black, this makes the whites of your eyes look brighter!
When your eyes water when you're tight-lining your waterline, sniff hard through your nose, it pulls the tears from eyes back into your sinuses and stops them watering everywhere and ruining all your work :-)
MAC Fast Response eye cream is brilliant as an eraser for under-eye uh-ohs!
Don't look straight at a mirror to draw on your eyeliner. If you hold a mirror at chin level, you'll naturally look down, so you can see your lids and draw a quick line with no problem.
Don't use kohl or other pencil liners with false eyelashes; the grease in the pencil can cause the glue to loosen and the lashes to detatch. Water-based liners are better with false eyelashes instead.
In general, I only put a stickier formula lipgloss in the middle of the lower lip, as it tends to migrate to the edges anyhow, and applying it all the way to the edge can make you look (after a little while) like you're drooling!
Dab some peppermint extract on your lips to make them temporarily pout.
Add a frost or glitter pigment to some MAC Fix+ in a little spray bottle. Shake it well and spritz your face, hair and body to give a great sparkle for the summer, for party time or night-time makeup.
Fed up of your glitter disappearing after ten minutes? To make sure that your eyes hold onto eye glitter, use something like Too Faced Shadow Insurance Glitter Glue beforehand, apply the glitter, then seal in-place afterwards with something like Benefit She-Lac (discontinued now though) or Eve Pearl Shadow Mix & Seal.
To flatten an erupting breakout: first ice the blemish for 30-60 seconds to decrease the inflammation, then use a cotton swab to dab hydrocortisone on the bump (this makes the blood vessels constrict, which helps to minimise redness). Conceal after this.
For super-oily skin, Milk of Magnesia is a godsend. Apply all over your face, then wash it off and continue as normal. This helps makeup to stay on excessively oily skin. It can give a white cast though, so remember to warm up afterwards.
Stuck? Olive oil is great for remove particularly stubborn eye makeup, and it shouldn't irritate your eyes.