I don't believe in reinventing the wheel, so provided that it is appropriate under FounderDating's T&Cs, here's a good discussion in Quora: https://www.quora.com/When-should-I-incorporate-my-startup
If you're working alone, Eric's advice above is good to follow. But for everything else, it isn't just about limiting your liability, but being able to obtain the commitment of cohorts. Most major law firms have a startup program that defers any billing collections for a year for your startup, so there's no excuse not to seek what will ultimately be advice vital to your success and scal. I personally like WSGR's program (no affiliation), but that's Valley specific. Accelerators can also be a good source of finding a trusted lawyer affiliation. Make no mistake. Not every lawyer is good, let alone great, so get references. It's an important relationship.