There are many different wood joinery techniques such as tongue in groove, biscuits, dowels, etc. The more complex the joinery technique, the tighter the joining pieces of wood will interlock. In almost all cases, glue is used to further strengthen the joint.
The strength of the glued surface is dependent on the degree of contact on open grain surfaces. In many cases, it's easy enough to get a good spread because the surfaces are narrow. Just squiggle a bit of glue on both pieces, mate them, and that act will naturally distribute the glue evenly. Then just wipe off the squeeze-out.
But what if the pieces are wider? This is a bit more problematic. But a tip from Woodworker's Journal has come up with a very slick method to remedy the situation. Simply apply the glue in the typical snake pattern, and then use a threaded rod to roll it out to evenly coat the entire piece of stock evenly. Then mate, clamp it up, and let it dry.