I haven't been knitting for too long, but here are some of my tips anyway-
a lot of those gadgets they sell you don't necessarily need esp. the st holders and the markers, yarn and safety pins work great as well as those tiny hairbands or rubber bands
I keep all my straights in a wine carafe and this way they don't get lost or bend
if you have to unravel a row, get familiar with the correct way to reinsert your needle into the sts so that they don't twist
always leave a long tail
if you are running low on your yarn and wondering if you have enough to do just that one more, check to see that your yarn is four times the row plus about 6 inches for a tail
I have found that lots of row counters/st counters are not a waste of money, it's nice to have more than one for several WIPs
when you want to substitute the yarn, look at the needle size for the pattern and look for that same gauge on the label of the yarn
when you have to make a portion of the pattern twice, like sleeves, and you are not knitting two at the same time, count the rows and mark it so that you can be sure they are the same length when you go to sew up
Mattress stitch for just about everything
def. get some darning needles
matching embroidery thread is excellent for sewing on buttons- regular thread is too thin and yarn is too bulky
go by the measurements in a pattern and not the size
buy a large size bulletin board and lots of non-rust T-pins for blocking
always do the gauge, esp. when you are just starting out
read the pattern all the way through before you start knitting it so that you don't find out about something you should have done until it is already too late
also, if you don't want a bunch of loose ends that you will have to weave in, you can knit the first four or three stitches with the tail and then cut it off once you are done blocking the project you are working on
Hope these tips are helpful from a knitter who is just now learning all the tips herself
