You can have a lot of fun with a good pencil. That won’t necessarily make or break a piece, but it can be hard to do good work if you have bad materials. The best pencils have leads that make a dark, smooth line, don’t have a lot of hard chunks in the lead, are easily sharpenable, and are centered in the wood so they sharpen properly.
You may consider trying a woodless graphite. They are pure graphite wrapped in a tough outer coating. You sharpen them just like a pencil but the whole tip can be used to make lines! They come in an assortment of hardnesses. My essential set consists of a 2b or Hb, a 6b and a 9b. Layout is done with the 2b and the shadows are filled in with the darker, softer 6b. Woodless graphites cost a dollar or two each and last a very long time.
Don’t forget a quality mechanical pencil. It can be invaluable for making crisp fine lines. Buy a good one and it will last forever. A good one can be had for less than ten dollars in the drafting section of an office supply store.
Or just shop at Dick Blick – they’re awesome.