This has come up a couple of times recently, so here's a reminder to those wanting to get on here:

Bidding should be considered a chance to bid days on/days off only. We have no trip/bid protection. No matter what you've been awarded, Scheduling can and will change your line at their choosing. Seniority has no effect (ask me how I know!). Budget for guarantee and be pleasantly surprised if the company allows you to go over it. Layovers are an exercise in wishful thinking. By all means, bid a line with attractive layovers, but don't plan on it until you touch down. Saves a lot of frustration when you look at it this way, and it's hard to internalize if you're coming from the regionals, for example. That said, some flying tends to stay together, such as DHL routes, but I get bumped off those too. YMMV