I used to feel the same until I thought that meh, I scrub up okay too and just can't be bothered with competing these days (for anything other than a special day/night out, I've not let myself go completely). I now have the attitude that they look lovely (sometimes) but I have better things to do and my it looks hard work to stay so groomed.
I had a consultation from a funky young Mac girl who 'matched' my perfect lipstick for me... it was gopping, a kind of sludge colour. Pick something you like the look of, ask the assistant to apply it for you, take a look and if you like it buy it, if you don't, pick another colour you like, rinse and repeat until you're actually needing help choosing, then ask for advice. I spent a lovely 45 minutes in a store only the other week, came away with 3 lipsticks that the assistant hadn't recommended, one that she had, and about 6 that we'd tried and said 'ew' to (4 of them were her choice).
OldLadyKnowsNothing what colours do you LIKE, what colours make you feel good? Start there. I like beige (seriously!) but Beige doesn't like me, and therefore makes ME feel rubbish. Try try try again, take a friend you can trust, if you have a DH/DP, reserve a few items that you've tried and aren't sure of, then return to the store with him, and see what he says.
Successful shopping in my experience is either bloody good luck, or a process of elimination, and I've never found the 'perfect' outfit by just one person looking at it. Good luck though... get your outfit first, make up after. Take your outfit with you when you look for make up. And if shop assistants look at you like you're a PITA/nutter, give them a withering smile.