In general Trent's behavior is quite laid back, and he speaks with a soft voice. Trent never wears a watch since he's always late, so watches depress him. Despite his laziness, Trent does care about and loves his little sister Jane and often wishes to help her in any way.
He takes weird things in stride, like being in a band with physical holidays or strangers in his house. He is also the most stable of the band members and puts up with their arguments and bickering. He usually hangs out with his fellow band-mate, Jessie.
Despite knowing about Daria's initial feelings towards him, never acted upon them, treating her in a gentleman's way. After getting over the crush Daria sees Trent as a good friend who has won her trust.
Despite his lethargic tendencies, Trent can be somewhat insightful. He gently coaxes Daria to Jane's room in The Misery Chick after the latter had instructed him to send everybody away because she wanted to be left alone. He helps Daria figure out her relationship with Tom Sloane (after she had gotten over her own crush on Trent). He is very close to Jane, and tried to convince her not to go to college because he would be lonely in the Lane house by himself.
He also has an on-again-off-again relationship with Monique, lead singer of a local band called The Harpies. In Lane Miserables, he admits that he is scarred by the fact that his mother, Amanda, didn't go look for him when he decided to live in a tent in the backyard.
During his non-waking hours, he likes to practice. He's been known to practice the opening to "Come As You Are" for hours, and when rehearsing his own songs the volume is cranked to maximum. He can also get distracted by random things, such as the novelty settings and tunes on a keyboard or comparing vinyl to CD (without realising he's listening to the radio instead). He even sleeps with his guitar, which he and Jane joke is counted as practice.
He also spends his time trying to invent lyrics. He can be inspired to start talking in lyrics or writing them, at any time or place. This too is another bad habit he has while driving, and in conversation (he once started doing a song about betrayal right after he'd tried to reassure Daria that she hadn't betrayed Jane).
While he can play the guitar well enough and nobody has ever commented negatively on his ability to play, his lyrics are usually quite inane. Songs have included lines like "you're cutting off my nose to spite my face/OW! My nose!/OW! My face!". Every song is designed to have simplistic rhymes. Jane has made snarky comments about Mystik Spiral's abilities and chances, and even Trent himself (Jane's Addition) once said that the songs in the band's second set were "just the ones that weren't good enough for the first set" and that he'd leave if he wasn't in the band.
Despite this, Mystic Spiral keeps getting gigs at The Zon and other places, and grunge fans seem to like it. (This is likely a piss-take on the grunge scene at the time)
Trent is usually enthusiastic (as much as Trent can be enthusiastic) about his music and the band, and will make grand statements about their future and their artistic merit. "Road Worrier" and See Jane Run showed flashes of doubt and angst, however: in the former, he worried he might fail, and in the latter he expressed discontent about the state of his career, referring to club audiences as using "[his] the backdrop to their pathetic mating dance... they just want something loud going on so they don't have to talk".
The only time Trent genuinely had the proper inspiration going and he came up with a song which wasn't corny was in Lane Miserables, where the close proximity of his parents and siblings were beginning to drive him crazy. His song "Psychic refugee" came out naturally as an out poor of his emotions.
According to Art Burn, Mystik Spiral never play cover songs as that would undermine their creativity.
Daria has a crush on Trent during the first few years of high school (aka the first three seasons of the show). She fears embarrassing herself in front of Trent, which causes Jane Lane to deliberately leave them alone together multiple times. Trent is pretty oblivious to the crush until That Was Then, This Is Dumb, & then does his best to not lead her on.
Despite being very complimentary of Daria, he tries to avoid her so he doesn't embarrass herself or him. However, Trent also uses the crush to his advantage; at one point he outright flirts with her in order to get her to pierce herself. By the end of Jane's Addition, it becomes clear that they wouldn't work out. Despite this, Trent greatly respects Daria's opinion & advice.
In the future, Trent has broken up with his band, Mystik Spiral. He's not exactly successful, nor well-known by any means, he is a part of a functioning band called Trent Lane & The Mystik Explosion. He lives in Queens with his four bandmates (assumed to be his better friends from Mystik Spiral).
Trent is alright financially due to the money from his most successful hit single, Freakin Friends, but ultimately has to moonlight as a bartender in order to make ends meet. His favorite sibling is still Jane, & the two still spend time together, with Daria occasionally joining them. Things are no longer awkward between the two of them, & they've put the past behind them in order to embrace a new adult friendship.