I use my ole Barlow pocket knife VERY carefully not to gouge the aluminum. On the seal surface just wipe with carb spray cleaner on a rag, Do the same on the block and cover gasket surfaces to remove any oil.
I spray a lite coat of paint on both sides of pan/side cover gaskets and install while still tacky. Once the engine heats up the first time that thing is sealed snug as a bug in a rug. The use of gasket sealers can change crankshaft end play specifications.