Raising your Level
Play for tips as much as you can. Take a gig as often as possible as your Sim needs more experience doing them in particular. It's one thing to do the tricks, but another to perform the show. As you perform in the streets, Celebrities will be in your captive audience from time to time. As a result, you'll naturally gain Celebrity status in town and sometimes get gifts from this without putting for any effort.
Performing: Gigs
As you level, Proprietors at venues available to you will appear on the map. If you select 'Audition for Gig' by clicking the owner, your Sim will do a trick for them. In general, if they succeed you'll get scheduled for the next day in that place's regular slot for performers. If the next day is already taken by a scheduled gig, it will go on to the first available day. You can schedule up to seven gigs, one for each day, at level eight. In general, it's better to leave your schedule somewhat open and pursue only the best gigs you can get. Missing gigs shouldn't be a problem. You are given a warning two hours before in the notification area, and if the Sim isn't doing anything you queued, they will head to the gig to be on time.