Assuming you're not using both the friction and manual feed settings simultaneously, there's really only one adjustment you can make: Reset the clear plastic paper guide that mounts on the ribbon carriage assembly.
The rule of thumb is: Loosen the paper guide and put your four-part form and one additional piece of paper through the printer. Press the paper guide up to the mass of paper--not too tight--and tighten the guide's screws. This gives the proper clearance for the four-part form plus a slight amount for margin-of-error. You may also have to run your forms with the paper bail up (not riding the platen).