Not a pro but a advanced amateur
When you have 3 way switches there are several different ways they can be wired together. The most common is where you have a 14/3 (3-wire, 1 ground) that runs between the 2 switches. The master switch switch takes power in on the common terminal and then directs power out of one of the two output terminals depending on the switch position. The 2nd 3-way receives power on one of the two terminals and then depending on its switch position will direct power out of its common terminal to the fixture.
Probably the best thing to figure out first is to match up your wiring scenario to one of those listed on this page, then you can figure out which way things should be wired together.
3 Way Switch Wiring Diagrams | Easy to read wiring diagrams for do-it-yourselfers
If you have 14/3 wiring running to the fixture and you wire things up wrong you can get the entertaining scenario where depending on switch position you can have either the fan running or the light turned on, but never both, and you can't shut them both off