A good beginning in basic plastic toy restoration is the Mlp Restoration Project; it covers some basics like
General safety precautions, what materials you can use, etc,
Rehairing, restoring hair, hair care, etc.
Restoring acessories and playsets through paint, scans of stickers, even repairing some cardboard packaging,
Restoring plastic, like removing pony cancer, rust removal, stain removal, even restoring missing parts,
Dyeing plastic, painitng tips, and much more!