The person who does the most research and homework before the season has a huge advantage over everyone else in the league. Be prepared for your draft, and have your rankings done early so you can update them throughout spring training as necessary.
The first step in making rankings is to project the stats for each player. Start with a list of the players at each position and methodically project their stats for this coming year. Look at previous years, split stats, team changes, injuries... This is an extremely inexact science, and any projections within 65% accuracy are generally very good.
Also trust your own personal opinions about players. You may only be a FBB rookie, but following the crowd in fantasy baseball will only produce mediocre results. Dont be afraid if your projections for certain players differ from the consensus stats.
Lastly, have confidence going into your draft. If you have done all the necessary preparations, including a couple of mocks, then the draft should be no problem.