Aligning multi-color woodblock print?
My bachelor's degree was in Fine Arts, with a focus on wood block printing. 

The technique I was taught involved marking the center line on the back of the leading edge of the paper. (The end that will feed into the press first.) On the press, lay out a registration paper that clearly marks the location of the block, a corresponding center line, and one or both leading corners. The block is inked and laid on the slab. Then, align the center lines and corner marks, with the other end held high. Slowly "roll" the paper flat onto the block while keeping the leading edge aligned. This minimizes inappropriate contact and ensures a flat lay on the block. The ink will loosely hold the paper in place.

Once the paper is laid, heavy felt blankets are usually laid over the entire thing. There is the chance for paper movement here, so again - a careful "rolling" action from the leading edge back is best. Make sure the weight of the blankets is centered over the block as you do this. These blankets then keep the paper in place while printing, as well as enhancing print quality and embossing.

Ensuring that your press is set to the appropriate height is very important too. Too much pressure will cause damage to the paper, or movement of the block and/or the paper. Once printed, the blankets and then paper are removed in a similar but opposite method.