Everything Saf said.
Cutting and pinning are important. Make sure your pattern and fabric are pressed and take time pinning and cutting. I spend a lot of time fiddling not only when pinning to cut, but pinning to piece the item together. If it's well cut and pinned, the pieces will go together accurately and won't move, slip or slide when sewing.
Pattern instructions can be vague. Saf mentioned having a good book. I have the Singer Complete Guide to Sewing and it's fantastic. It explains everything to pattern layout, reading pattern instructions, talking about fabrics, stitches, fastenings, etc., etc., etc. I refer to it frequently and even if the instructions are rubbish, you can usually work your way through it!