Location
You cant catch what isn't there. Location is ALL important. You might be able to bring fish to you with bait and flavour etc, but being mobile, or doing your homework will pay off greatly. This is the part where I usually try and use my intuition.
Bait
Fresh baits fish best. (unless your after eels :-) Use fresh baits. Simple. And simple baits are best. The usual suspects like bread and sweetcorn and luncheon meat are hard to beat as all rounders.
Presentation
Use the right line rating for your rods, and match your hook to your bait. Hooksize in my experience is not as important as you might think. I caught a 2lb carp on a huge hook meant for catfish, fair and square in the mouth. Its the presentation that counts, so match the hook to the bait, NOT the fish you want.In other words, even if you are after large carp, using corn means use a smaller hook.
The bait dictates the hook.
Confidence
Cited time and again by many professionals as the main thing to take fishing with you. Anything that gives you confidence in your fishing, can only improve it. Don't be afraid to try new things of course, but using methods and baits you have faith in gives you confidence, and that has the biggest influence on your fishing.
Intuition
You've got it. Use it. Your're an animal, not a robot. Learn how to tune in and 'Listen' to your gut feelings. Countless times Ive gone with my intuition, and fished so much better than when I tried to do it 'by the book'. Also, something I often tell myself is the tag line from Stormbaits lures - "think like a fish, no matter how weird it gets" :-)
Sound and Sight
Just like a submarine captains first lesson, never forget, that SOUND KILLS. OK, you wont get depth charged on the bank, but making much more than a whispered conversation, or the lightest of footfalls, is a good way to kill your fishing badly. Also keeping a low profile and not waving rods, brollies or arms about on the bank over the water, will avoid spooking fish. If they don't know your there, they will come in close. :-)