Vaseline, Dawn dishwashing soap? Also, make sure you relax the finger when trying to remove it. If it is causing a circulation problem, have a jeweler cut it off.
The safest way is to cut the ring off. This is an alternative but should only be attempted if this isn't an emergency. Why is your ring stuck on your finger?
Depending on how swollen it is... it may need cut off... particularly if its swollen in the area the ring is... as blood flow would be restricted. I had to have that done several years ago... injured my finger where it took several months to return to normal... cost $50 to have the ring cut and later repaired. ( 14k gold)