While 78s are fragile and tend to warp as well as do other things they're not supposed to, there are ways to get them into better shape.
For warped 78 rpms, place them between two sheets of glass. I don't recommend putting any additional pressure on them, though. Leave like this until they're less warped.
If the label of you 78s are dusty or dirty, use a dry brush to clean them. Don't ever use water! This can cause the label to bubble, diminishing the value of your 78 rpm.
For washing the records themselves, don't ever use alcohol or heavy abrasives. A soft soapy mixture is best. Make sure to not go against the grooves when cleaning the record.