Since a student pilot posed the query, here are some various thoughts based on my experience with FF. I'm a low-time VFR pilot (500 hours). I rarely make short flights; mostly cc for 1-3 hours. (I wouldn't typically use FF for a 30-min hop). I consider FF a HUGE privilege that could easily be taken away if enough GA pilots abuse it, neglect it, or don't take it seriously.
I always use FF at night. I highly recommend that. I do a lot of night flying.
If I'm flying thru or even near Charlie airspace by day, I use FF near and thru that region.
If I'm flying near or thru Bravo airspace by day, I use FF for the entire flight.
I have never been refused for FF. Maybe it required a 2nd request a few times, but never refused.
Make sure your transponder is kept in good working order and calibrated according to your AD once you get your own plane. If there is an issue with your transponder, FF may ask you to ident, and if they still can't establish a fix on you, they may ask you to recycle your transponder (turn it off, give it 5 seconds, turn it back on, let it re-set.) Never do this unless asked or without asking their permission. You drop off their radar completely for several seconds, and if they're not expecting it they'll rightfully freak.
It's very easy to miss a call from FF if you're talking with your passengers.
I inform my passengers that I'm using FF and I either need to isolate myself or limit discussion. Most of my passengers love to hear the ATC chatter.
Don't refuse a "request" from a controller unless it creates a safety concern. For example, I've been kindly requested to veer around a busy corridor near Louisville at 11 pm when UPS has taken over the airport. (Why would I say no?) Understand if you're not in the corridor or in the airspace, FF will "request" rather than "demand." Tell them you'd be happy to. It will probably cost you 90 seconds. Remember you're the smallest guy they're watching. Respect that!!
Whenever you hear your tail number called, put your right hand on the frequency dial before they say the next word. Nothing annoys FF more than low time VFR pilots asking two or three times to repeat a frequency when they are handing you off to the next sector.
Learn which FF calls MUST be answered and which don't. You'll probably learn mostly by trial and error, but you can get in far more trouble by saying nothing than by offering a quick, "937 Affirm." When they say, "937, traffic at 10 O'clock, 7,000 feet. No factor." you don't have to reply ... but why not? "937 Roger." It's a lot like being reassured that your teenager didn't fall asleep in the middle of a conversation.
I never fail to affirm a frequency change on a handoff ... I don't necessarily read back the new frequency ... just "937 Affirm. G'night." If they go looking for you, they have reason to be annoyed. I've been the "annoyer" before.
Always help a controller who is asking you to help find a missing pilot. They'll love you for it. (If you ID yourself as a student, they likely won't pick you to ask for help) That's reason #267 to always keep a pen handy ... a semi-panicking controller who says, "937, can you do me a favor? Go to 123.475 and see if you can find N654 Mike Papa. He never terminated radar coverage and we can't find him." It happens. More than you'd think. Drives the controllers crazy.
ALWAYS advise on your altitude changes. They'll usually say, "Maintain VFR and advise of any altitude changes." Again, it will drive them nuts if you start a descent without advising. When you advise, they will always verify and usually thank you.
If you're using an intermediate waypoint such as an airport or VOR, let FF know it if it's far enough off of a direct route to your destination airport that it could cause some confusion. 04º ... don't bother. 25º ... bother. Same goes for deviating around weather. Chances are they'll let you know of the approaching weather before you see it, but do all you can to make their job easy. Beat 'em to the punch and they'll appreciate it.
Once I'm within 15 miles or so of my destination airport, I often get the feeling that FF is reeeeally wishing I'd terminate radar so they can get rid of me ... but since a lot of confusion and bad things can happen on approach, don't terminate FF earlier than you feel comfortable. They'll want you to tell them you have the weather and the field in sight when you terminate. Whether it's legal, proper, assumed, or otherwise, when you advise, "Indy Service, N937 has the Indy Metro weather and field in sight" they will immediately respond with their "termination" spiel. By day, I typically do this 8-10 miles out. By night, especially with any weather, rarely before 5-6 miles out. When you start flying RNAV/GPS or ILS approaches, that's usually the intermediate approach fix.