I have one female that's on a 6 month cycle, one female that is a year old and I have yet to see a heat cycle, and two females on an 8 month cycle. Sooo... they are all different. The female on the 6 mo. cycle doesn't even bleed, but my 'fixed' male just starts loving her to pieces when he normally doesn't have a lot to do with her.
The other two bleed a very tiny bit and uaually keep themselves clean. One of my females had a false pregnancy on her first heat, but I knew it was false, as we didn't breed her. She started swelling like she was producing milk and even got big. It lasted about 3 mos! But she has normal heats now.
Anyway... just keep an eye on her. It's different for everyone. And 'spotting' is usually the first sign. She'll do that for several days and then the 'heat' starts. That usually will last about 1 week. They can get a little aggressive also, so if she starts acting different, that's probably a good sign.
I'm sure others have other things you can look for.