Here is how I do it... Keep in mind that I didnt take the time to book match these 2 pieces of walnut. I am doing this for demonstration purposes only.
First, I got a piece of granite countertop...a cutoff piece that is 1.5" thick and dead flat. On top of the granite I attach a piece of self adhesive sandpaper.
Attachment:
granite.jpg
Next, I hold both pieces of wood to be joined together and rub then on the sandpaper, holding the wood by the ends and with a end to end motion while pressing down on the sandpaper.
Attachment:
sanding.jpg
Then when I think it is sanded so that both sides are flat and smooth, I hold them up to a window, pressed together and check to see if I can see any trace of light between them.
Attachment:
window.jpg
If I see light, I sand some more until all light is gone. If there is no light showing, then I go place the 2 pieces of wood on three 24" pipe clamps, glue one side and spread the glue, then clamp the halfs together until I see squeeze out all the way down the seam. It works every time. The only hting you may have to watch for is that you want just enough clamping pressure to hold the wood together. If youuse too much, the wood may tend to bow on you. You can use your finger to make sure the two halfs are in line with each other and loosen the camp and press the wood down flat on the pipes to bring them together. I always let my joints dry in the clamps overnight... just for a secure joint.
Hope this helps!
Ken