Ok so not sure if your asking for advise on what brand of paints to use or just techniques but i would just go with
GW to be safe and be sure you can achieve the looks you want, the only real criticism is the price but you do get good stuff for it.
as for colours:
black spray for base coat
chaos black and skull white
boltgun metal for all your silvers
red (blood or scab red), yellow (a slightly darker, golden hue is best - cant remember the names of the colours for yellow) and blue (ultramarines has a toch of red in the mix so go for the slightly darker enchanted blue instead, i think its called enchanted) - these are your primary colours, if you ever need any other colour you can mix it out of these plus black or white...
then you need to identify which colours you will use most. for orks: scorched brown, snakebite leather and snot green are a must. its hard to mix brown so you get two shades of that and the green is well... totally necessary
optionals to make life easyer:
foundation colours - orkhide for green can be nice to build tones and the yellow foundation (again not sure of the name) will help a ton with your yellow areas as yellow paints can be watery, but the foundation will help with that.
inks - devlan mud and/or thraka green - easy toning, awsome results and the best thing
gw make paint wise
IMO.
for tecniques - just search the web for tutorials im sure there are loads but one simple tip is that you start with dark colours and build up for there to brighter ones - its the logical way to go about painting minis and leaves you with good shadows in the recesses and allows you to place fine highlights on the hard edges of your model.
any specific questions you ever need to know just post up here or separately in the forum, people seem to be really good on dakka when it comes to this kind of thing.