Always take photo's before taking something apart for the first time, and lay the parts out in the order you take them off. When removing wheels, put the spacers and any other parts back onto the spindle as you remove them and replace the nut so that the parts can't fall off. Also when removing parts such as brake callipers or even cylinder heads where there are different size bolts make a simple cardboard template and put the bolts into it as you take them off, this will ensure you put them all back in the right order. It is also a good idea to refit the bolts when possible into the frame/engine so they don't get lost.