Usually an act should be no longer than 45 minutes unless you're Now You See Me then you can be several hours long and give your audience millions of dollars.
45 minutes is the length of the typical performers' show. . . especially if they're doing big illusions.
Christopher, Formula and others have given you some nuts & bolts to chew on. The one thing they didn't say (that I noticed) is that THIS IS A BUSINESS and in creating your product (your act/show) you need to look at it as such. . . and yes, that includes those weekend warriors that only work part time at this stuff (a.k.a. Semi-Professionals).
If you were in the position to hire talent you would be looking for certain qualities but most importantly, you would want to know that they were approrpriate to the event or situation you were bringing them in to. . . asking Mike Ammar to do 2 hours on a grand stage might not be a successful venture but inviting Greg Wilson to do the same. . . well, nothing more need be said.
Start with where you live, your age, knowledge base and resources (inventory).
Look at what you can honestly deliver right now and what sort of market base that type of menagerie is best suited to; Kids? Grown-ups? Business Groups? Freak shows?
Though I tinker most of what I do now days is Seance type work and the telling of ghostly tales that means that I work with small groups (usually less than 18) under intimate conditions a.k.a. close-up/parlor. I also pander to the over 30 crowd in that they are the folks with the free cash flow and living situation that most well suits the work I do and too, these are the folks that have a more mature interest in this particular mode of amusement. They hire me because of my age and knowledge. . . not of magic but of Magick. . . the metaphysical and esoteric.
Why would someone hire you? What do you have going for yourself?
These are the things you need to mull over in your mind and for best results, on paper.
An exercise Peter Pit used to run me through went something like this; think of a market you want to work in and using only what you have in way of skill sets, knowledge and resources, create a program that would be entertaining and appealing to that group. The catch is, Peter would have me do with with numerous different demographics so I'd learn to see a couple of important things; a.) how to use the same basic program and just slightly twist it so as to fit each demographic; b.) how to be more resourceful when it came to adapting my programs in situations such as dealing with young kids vs. teens vs. adults of various ages.
Play around with it, you've started off on the right foot by asking.