A serious danger I mentioned before about time traveling is the potential to become unstuck. In particular jumping around a lot at one time can really loosen your bonds to the point where you have to actively keep yourself grounded in one place. Once you become completely unstuck it becomes rather difficult to become grounded again as you've lost your anchor as it were. Sometimes luck will pull you back to a timeline that's naturally pulling you to begin with.
I happened to lose my control not so long ago and got pulled into a different timeline, suffice to say I was more than a little freaked out. It turned out to be just last year 2011, and it was a timeline I'd never been to before but apparently is quite close in proximity to mine or an offshoot. Interestingly though it was a timeline where I hadn't existed, something that I'd eventually expected to find but this was a first experience. My current thought is the version of myself in that timeline wiped himself out from it and the end result was the timeline now having a substantial void tried to correct this by pulling me from somewhere else. Though in talking to people I expected to know me apparently there weren't any shadows left and I was just a complete stranger to everyone. The whole experience though was very weird still, there was just something off about the way everyone behaved. I was partially inclined to believe it might have been a strange dream if it weren't for the fact I was awake when it happened.
The important thing I had to remember though was jumping away would be dangerous at that point, lest I destabilize myself further and become unstuck. So I stick around and interact, see just how different things are. I got to see some people that were dead in my timeline which was nice. Then after a few weeks I popped out back here. I've been to timelines before where I was dead, and attended my own funeral, and those are always interesting. Though they don't compare to a timeline where you just don't exist. Though this also brings up another good topic of meeting yourself. Like I mentioned before it's no big deal, but if you're trying to be more inconspicuous rather than coming off insane I suggest having a prepared back story. Usually a fake name will do but be prepared to answer some standard questions like where you're from and who your parents were. Be sure it's something you've rehearsed well, it helps if it's true for somebody you know in your timeline. Try to stick to the same one so it's easier to remember all the details if you're in an area for an extended time. Once you meet yourself one of you will probably want to hang out for a while and show you to their friends.
All this having been said, if you do come unstuck always try to return to your point of origin. Usually your last anchor is the strongest and is you best chance for return. Once you're back, you have to stick around for a few weeks without jumping and actively keeping yourself in one place for everything to settle down. It also helps if you actually stay in one physical location as much as possible, which you'll feel like doing anyway because it can be very disorienting when you're not in control, and will make you very dizzy while moving around. Be sure to eat plenty wherever you end up though, you might puke it back up but the more you immerse yourself in a world the more anchored to it you are. My personal suggestion is lots of fruits, like oranges, bananas, and apples. If the timeline you're on doesn't have these things stick to anything with decent citrus, iron, sugar, or protein, and plenty of liquids. So far the one thing I've found to be on almost every timeline is star fruit and I would suggest it as a last recommendation beyond that there isn't anything specific I can say works well. Sometimes fish helps, sometimes it doesn't, and I haven't narrowed it down to any specific kind of fish, so it depends on timeline really.
As to the warning signs of becoming unstuck, it's the apparent loss of time, you think it's a few second but it's been a few hours, and in truth it's both, in the process of coming unstuck you can wildly move through time within your existing line. This is both forward and backward though so be warned. When you start jumping lines it always starts in the extremities, you'll feel it in your fingers and toes first and by then it's too late all you can do is brace yourself. You usually get pulled to a nearby timeline or a different time where you have a stronger natural pull, often it's places you've been before or somewhere in your natural timeline. And my last piece of advice is stay away from physical locations you've jumped to or from before, the zones themselves are easier to jump through but it's for that very reason they're also easy to become unstuck in. I haven't heard of a zone itself ever becoming unstuck so you don't have to worry about people accidentally jumping with your or after you or something, but the more you use a given location the easier it becomes in that location so I'm not sure if it's just a weird psychological thing or if you're actually effecting the world in the process.
I'm also taking the opportunity to revise a previous statement, that while you could bring simple objects you couldn't bring complex ones, well I accidentally came back with a cell phone from a different timeline recently and now I'm starting to think I can bring back a lot more. Though I doubt I'll be trying to bring back much it definitely warrants further testing.