First off, what do you mean by professionalism? Playing more in clubs, or continuing mobile gigging but without the shocked looks of customers?
I am gonna concentrate on the latter, since for me a wedding DJ can be any bit as professional as a club DJ.
Dress the part is where I’d start! Especially for weddings. You want to meet the couple up front (by the way, the Wedding DJ course on this site is awesome reading!). Don’t show up in shaggy jeans and t-shirt. No need to show up in a suit at that time, but chino’s and a pressed polo or dress shirt with a pair of decent shoes/loafers (no sneakers or VANs) should do the trick. Be sure you are freshly showered, hair combed, brushed or whatever it is you do with it.
Remember, these people are shopping for someone to make their most important evening of their life work!
At the gig, you DO show up in appropriate outfit. If not a suit, then at least a very professional outfit (I don’t like a suit jacket when playing, so I will usually wear a vest, but I make it stand out. Don’t want to look like the waiters, you ARE the creative DJ after all. But I will wear dress shows, a tie (have been known to don a bow tie in the color theme of the wedding 🙂 ), dress shoes with a good shine and generally make sure there isn’t anything to make me stand out from the crowd (who most likely will all be wearing their best suits) in a negative way.
Especially with the “handicap” of youth, appearance is everything. You can help your credibility and image by not looking like a high school kid.
Obviously at house parties things are more relaxed, so so can your dresscode. Back in the day, I’d always make sure I looked sharp even at a friends party I’d try to have my version of the “DJ Look”.
Greetinx.