Lets start from the top:
Go down to your nearest big box and find the longest (12 or 16 footers)
2 x 12's you can get your hands on. These will be the clearest and straightest boards. At 9 or 10 dollars a board we can be a little wasteful and choose to avoid knots and defects.
Cherry pick through the pile and sight down each board. Its okay if all the contractors think you are crazy. You can build this table from two 2x12x12', so why not take the time to get the best material.
What you see to the left is what we are looking for, a center cut, flatsawn board with marked cathedral grain down the center and straight grain near the edges.
We are looking to keep as much of that quartersawn material on the edges as possible. That means we will rip down the center of the board, dress our boards and when we cut to final width before glue up, we will remove material from the pith side of the board.
You may be asking yourself why even rip down the center, well most of us have a 6-8" jointer and in order to dress these boards properly it must be cut to fit the jointer.
next up, get your glue.