Once you get up to the Private and Large venues, you'll likely want to stop doing any regular gigs at the small time venues to open up your schedule for better paying Gigs. But even at this point, sing-a-grams are worth doing for some quick job experience if you have a day between Gigs. At this point, you should have a steady gig or two and will have plenty enough Gig options to keep you busy through most of your week. Sing-A-Grams jobs will be worth more money as you progress in level, so you won't outgrow them at least until you unlock Live Show venues at level 5. This doesn't give you more money, but it does give you a better chance of putting on a really good show and earning a regular weekly gig. You should try to set up your stage as early as possible (an hour and a half to two hours before your show starts) as this will start your show early. This allows you to go to your Gig location in the morning, and play for tips until you can set up your stage. Sing-A-Grams will keep you busy for most of the day, but on the bright side: you don't get them on a day you have Gigs (you'll occasionally get one or two after an early show). To effectively level your career as a Singer, you should grab every Sing-A-Gram job you can get once they really start coming in steadily and audition for every Gig available to you.
Ignoring Sing-A-Gram requests has no impact on your job performance. You could also forgo your first day of Sing-A-Grams and just camp out somewhere to perform for tips, and easily get your first career level on your first day. One of the best places to look is the Coffee Shop. You can easily get to level 2 in spite of this by playing for tips, and you can even supplement your income significantly if you find a good crowd. Don't count on this though: your average first day is about two jobs. The early pay for these jobs isn't that great, but the experience is and if you have a good first day you can easily make it to level 2 and unlock your first gig. They start around noon and can pop up at any time, until about 10pm (although they sometimes come up even later). Sing-A-Grams work much like Ghost Hunter jobs, where you get an on screen message that a job is available and an icon on the map. The job metrics for a Singer are delivering Sing-A-Grams, performing for tips, and completing Gigs. You start your singing career as a Sing-A-Gram Novice, and at level 1 you get access to two Sing-A-Gram jobs and a single song that you can perform. You'll have to select a Stage Name at this point, which can be changed at any time by clicking on your Sim. They will unlock the career for you, and you'll start getting messages for Sing-A-Grams the very next day. You'll usually find him close to the stage that you'll be performing on some day, but you can always click on the lot and select 'Call Over Proprietor' if he's not. You can usually take on this profession by looking through the newspaper or on the computer to see if the Singer profession is offered that day, but if it's not you can head to the big park and speak to the Proprietor there and he'll get your Sim started. While the money earned from the weekly stipend doesn't increase if you raise your Singer past level 10, each time you fill the bar the amount of money you get from Gigs will increase. This is paid out on Sunday, like any other profession. While Singers will make a majority of their living off daily jobs and gigs, they also get a weekly stipend based on your career level.
A singer should always be their own biggest fan! The Diva trait doesn't appear to have much of an impact on performances, either, although it does offer some interesting interactions with other Sims, and even yourself. You can use a guitar in your performances (other than Sing-A-Gram jobs), but it seems mostly for visual effect as even a singer with no Guitar Skill at all will still be able to put on great shows. Natural Born Performer helps out in this profession by improving the success rate of your gigs. You can play for tips, of course, but Sing-A-Grams will offer more early job experience and provide a steady paycheck. In this profession, your Sim starts out as a singing messenger, delivering "Sing-A-Grams" to various other Sims to help them celebrate an achievement of sorts (like completing a good workout or having a birthday), to raise their spirits after getting yelled at, to set the mood for romance, or to just tell them that they're special! This will be a significant portion of your pay and job experience throughout the early part of your career, until you start unlocking the venues around town. This guide is about the Singer profession that comes with The Sims 3 Showtime expansion. The Sims 3 Showtime: Singer Learn about Gigs, Venues, and Making Money in this Profession by Robert Kennedy (Hosfac) The Sims 3 Showtime Guide