I second the Kreg suggestion. Go ahead and get the actual Kreg brand...far better than competition.
To really do a first class top job, truing the lumber with a good table saw followed by surface planing can have a tremendous effect on fit & quality of the table-top joints. If you are going for super-rustic, you can skip the prep, but fit and unevenness can get quite crude with stock #2 material.
After longitudinal boards are joined for the top, trim each end with a circular saw using a clamped guide before attaching bread-board ends. I like to use a little glue along with the pocket-hole screws - strength is even better, and you can stretch the screw spacing a bit more.