The Working Together rules specify that:
A character can only provide help if the task is one that
he or she could attempt alone.
Moreover, a character can help only
when two or more individuals working together would
actually be productive. Some tasks, such as threading a
needle, are no easier with help.
The familiar has no special rules for this, so it can help with anything that it is capable of doing alone where help is actually useful.
Exactly which tasks suit these criteria is between you and your DM. You certainly aren't limited to only Perception and Stealth checks. In fact, it's probably impossible to help with a Stealth check, since no matter how quiet your familiar is, it won't help you be quieter.