In contrast to some of the respondents, I generally come up with a concept first (based on a general understanding of all the powersets) with specific powersets in mind, then compose the look and bio. I rarely enter the game without a firm concept in mind, and if I do so without a bio, it's only because I haven't worked out all the details yet. But they'll be there before they reach level 10.
I'm frankly surprised by the OP, I've been playing since this version went public (actually since 2006, and was online when they pulled the plug) and have yet to see any players in Homecoming on any shard who have bothered to create descriptions for their characters, except for one who (in ungrammatical English) apologized for not having "ideas" and instead left a bulleted list of possible origins for the character. I see characters with the "Roleplaying" title above their heads, but in my experience none of them are doing anything remotely related to RP and they don't have bios. I'm happy to discover that somebody is actually interested. Kudos to you.
I don't think you need "roleplaying hooks" in your bio, I think you just need an engaging character story (not just "angry guy from Hell looking for revenge" but more like "Jane Smith had a normal childhood, but then the Rikti invaded and she discovered abilities she never knew she had...", or "Mary Jones was an investment banker with a growing family when terrorists changed her life forever..."). Anyone willing to actually RP will pick up on that and play along. Good luck finding them.
(Bear in mind that I had some unsavory experiences in the original game with adolescent boys apparently acting on crushes on my characters, some [but not all] of whom were scantily clad, seemingly unaware that these are cartoons, and they had no idea that I was [at the time] in my late 20s with children and a completely unflattering body type. I did a lot of server jumping in those days.)
Taking a cue from UltraAlt, I had a few "homage" characters in the original and only recreated one of them here. All my bios are third person, but for homages I try to explain how and why they are different from the character they copy (they only look like clones). If the costume is the only thing resembling a published character (completely different backstory and abilities), I don't bother explaining why they look like a published character because the concept is completely unrelated. If I get "genericized", I'll just change the costume.