I'm more than happy to share some make up tips, but I will start by saying experimentation is key, my tips won't work for everyone and I don't like to recommend products as skin types and preferences vary so widely.
First of all it's important to select your products carefully. Avoid anything that claims to illuminate, highlight, reflect, give a dewy finish or contains any metallic pigments. They're great for flawless skin, but if you've got problems they'll just highlight them. Stick to matt!
Second, remember that foundation should only be used to even out skin tone, not mask flaws. No matter how bad your skin there are going to be some areas that don't need heavy coverage and covering everything with a thick layer of full coverage foundation will always look mask like. For problem skin I find liquid foundation is best.
Third, choose your colours carefully. This is so important. It's highly unlikely you'll ever find a foundation or concealer that matches your skin tone so don't even try to. Blend different colours (from within the same range) together to create your perfect shade. Start by looking at the veins on the inside of your wrists, do they have a green tinge or a purple tinge? How green or purple are they? If you look carefully most makeup has either pink or yellow undertones. if your veins appear to be green pick a yellow based foundation that's ever so slightly lighter than the skin on your face and another that's a few shades darker. If your veins appear more purple then do the same but with makeup with pink undertones. Personally, my veins appear very slightly green so I use a light foundation with yellow undertones and mix in a few drops of a darker shade with pink undertones to balance it out. Mix and match to create your perfect colour.
And finally, buy a good concealer. Once again, avoid anything that illuminates and stick to matt. Most make up artists wouldn't be without a dermacolor mini palette and with good reason too. It's a highly pigmented camouflage make up of the type used to cover up severe disfigurements, tattoos, burns, birthmarks etc. The mini palettes are great as you get enough colours to mix your perfect shade (especially important for concealer as your face isn't one uniform colour). You won't find it on the high street but it can be ordered online.
Ok, once you've completed your skin care routine leave at least 15 minutes before applying make up. It's also a good idea to blot the skin with slightly damp cotton wool/kitchen towel to remove any excess moisturiser etc before starting too. (I'm going to skip over primers etc as not everyone likes or uses them. If you've got one you like, great.) Start by applying a small amount of concealer with a brush to the areas that need it, starting in the center of any spots/discoloured areas and gently blending outwards, set with translucent powder and keep on layering until you've got enough coverage. Always start off with the tiniest amount of make up possible and add more layers as needed, always blend the edges away to nothing and always powder between layers. You're aiming to mix a colour that perfectly matches the skin surrounding the blemish.
Next, take a triangular make up sponge and tear it in half at the widest point. Using the torn rough edge apply a small amount of liquid foundation in a stippling motion, starting in the center of the face and working out. Don't wipe or sweep the sponge across the skin or stipple too hard and don't use your fingers or a brush, just gently pat the foundation on with a sponge to avoid disturbing the concealer you've just spent ages applying. Set with powder, apply the rest of your make up and you're good to go. Make sure you use a clean sponge every day, so either buy in bulk online and use a new one each day or chuck them in the washing machine in a delicates bag.
Two more tips. If you're having to cover large areas with concealer it's unfortunately almost impossible to avoid a mask like finish. So firstly, don't forget blusher (again, avoiding anything with metallic pigments) as it will help to mimic the natural variation in skin tone. Cream or powder is fine, but if you use cream pat it on (no rubbing or wiping) very gently BEFORE setting your foundation with powder. You can also try adding "imperfections". That mask like flat finish looks totally unnatural because no ones skin is that perfect. Try adding in a small freckle or two to distract the eye.
As I said, I find this often works well, but on the worst of days there's just no escaping bad skin. For me that's the days when the horrid painful cysts have swollen so much they've started to weep and scab over 
. Make up can cover the redness, but it just can't change the texture and for me, no matter what I do it always ends up collecting around the horrible scabbiness after a few hours. That's when I feel like everyone is staring at me and recoiling in horror.