What was posted earlier is all good advice. There is a thing or two I might add.

1. Try looking up a few premium pbfs of empowered characters. Paladins, druids, healers shamans. They all get empowered, so they follow a religion. You can see how they incorporated religions into roles and such, and usually there are some imm comments relative to their religious progress in there as well. Can be helpful if they are for an imm you are considering following too.

2. I followed one Imm, it was awesome. However, I went into it for no other reason than to follow the imm and be empowered. I think if an Imm knows you're doing it solely for the perks, they're going to be hard pressed to give them to you. But if you are engaging with the Imm and putting the effort in, I think perks will flow naturally. Just don't say I follow Daev, so I should get a 3rd legacy at 100 hours. It's not going to happen 99 times out of 100. Tattoos are rare, and they are earned.

3. Almost all religions come at a price. You may have the tattoo, but you'll have duties along with it. You'll be expected to hold the faith and preach it. I followed Ysaloerye. At first I swore off pills and potions. Later I gave up any magical armor. Then I had to cease travelling with or aiding any mage (not easy for a dwarf paladin). However, I was the first to reach the highest position among her followers, and that was an awesome feeling. Also, when you have a patron, they will snoop you far more then you know, so you better have the RP all the time, not just when you think they're watching. Or else you might find yourself on the wrong side of an imm's attention.

4. Can't stress it enough. Be respectful. They're taking their time to try and make you have a rich and full experience, but you have to put in to it as much as they do, or they're probably not going to want to bother. Have a role before you go. Have an idea about why you follow them. About how you can bring forth their glory into Thera. You are trying to serve then, just always keep that in mind.

Ultimately immteraction can be a very wonderful and rich experience, because imms have some of the best RP in CF. But you tend to only get out what you put into it. Don't come into expecting them to do you any favors, but give them a reason to want to watch and reward you, and usually they will.