The Infernal is the greatest threat any of us face. It preys on the instinct of a lot of kindred to try and grab power, of any sort, for themselves. Many believe they can later renege on the deal, but, remember where lawyers go when they die. There is no getting out. Once you're sold, you're sold. NEVER make the deal, no matter what.
I have fought devils on many occasions. The lesser ones inhabit the bodies of so called 'Infernalists'. Most of the time conventional methods are enough to destroy these scum and send them hurtling back to hell. Sometimes they come back. Kill them again and again until they get the message.
Most things you think would work on lesser demons work. Holy water, holy symbols, blessings, exorcisms. Do not bother usign fire, most seem immune. Magic appears to be able to affect them and many draw their power from an object or device associated with them.
Stronger demons usually seem to require some powerful ritual to get rid of them. This may involve the willing sacrifice of participants or a long, complex and emminently interruptable ritual. Remember, most demons cannot force you to do something, they must cajole. A soul given freely is worth far more to them.
If you find yourself up against the powers of the infernal make good use of mortal priests, the Garou and the Sabbat inquisition as they are very experienced in such matters and any alliance is worth it.