The vast majority of magicians have to do everything themselves. They develop the effects, write the scripts, put things together into a show, rehearse the show, market the show, book the show and perform the show. To become a professional (someone who gets paid for doing magic) you need to develop ALL of those skills.
Before I get into how to learn all that, there is something that Eugene Burger says in his book Teaching Magic. He says that magicians need a sense of urgency. We always think we have lots of time to do the things we want to do in magic. We don't. There is a concept called SMART goals. Goals need to be Specific (so you know what you need to do), Measurable (so you know when you've accomplished it); Attainable (make the goal something you can do, not something impossible); Relevant (make sure the goal is something important to your overall plan) and Timebound (give yourself a deadline). Setting SMART goals and working to meet them overcomes the sense that we have all the time to do things and focuses us on what needs to be done.
So here is the breakdown of the different things a professional magician needs to do:
Developing Effects
There are really just two components necessary to develop effects: knowledge and materials. At its most basic, knowledge is just knowing how to do the effect and materials is what you need for the effect. You can buy an invisible deck, read the instructions and perform the effect. There are lots of stand-alone effects that you can purchase and perform. You don't need to have an extensive knowledge of magic to develop effects to perform. On the flip side, you can spends years growing your knowledge of magical methods and develop your own effects or variations. My advice is to choose a number of effects that you want to perform for your show and go with that at the same time you are developing your overall knowledge.
Writing Scripts
This is probably the most difficult part of performing magic. The tendency is to present magic with "say-do-see" patter, where the magician says what they are going to do, does it and tells the audience to "see" the effect. Although this works, I think that to be a successful entertainer you need to develop better presentations because the say-do-see presentation becomes tiresome and causes the audience to focus on figuring out your methods (if the magician's focus in on what they are doing, the audience's focus will be on how they are doing it). Good books on scripting include Larry Haas's Transformations and Peter McCabe's Scripting Magic. Part of scripting is the development of your character. It is not enough to "be yourself" when performing magic. Your character informs the effects you choose, the scripts for your presentation and how you interact with your audience.
Developing the Show
This is where it all comes together. A show is a series of scripted effects presented in a pre-determined order. Most focus on openers, middle effects and closers, but a better focus is on texture, tone and flow. Texture is a term used by Eugene Burger to describe the variety of effects performed by a magician. That variety covers props (coins, cards, other objects), plots as well as the tone of effects. The concept of the tone of effects covers the type of presentation (say-do-see, story, meaningful, etc.), the emotions conveyed (joy, amusement, playful, serious and presentations that tug at the audience's heartstrings). Flow is how the variety of the show is tied together so that it is a coherent whole.
Rehearsal
Rehearsal is going through the effects with their presentations in the order you are going to perform them. It is essentially doing your show without an audience - again and again - until you are able to get it perfect 90% of the time and able to recover from the mistakes that happen the other 10% of the time so that the audience won't know that something didn't go right. Rehearsal is where you fine tune your effects, presentation and flow. The more you rehearse, the more changes you make and the better your show becomes. Rehearsal also is where you work out the logistics of how you set up and handle your props and transition from one effect to another. As you get to the final stages of rehearsal, get feedback from friends, family and even other magicians (I'd be glad to critique a video). Different perspectives can help you improve the show.
One important note -- I'm assuming you have sufficient performance experience. If you don't start performing a variety of effects (not necessarily the ones in your show) for friends, family and strangers to get that experience. That experience is crucial.
Marketing
Marketing is essentially getting your name out there. There are lots of ways to do that. My advice is NOT to start marketing yourself until you have a show to perform. If you start getting paid gigs before you are ready, your performance will not generate the word of mouth needed to kick start a career. I think the key to marketing is to have your performance and everything surrounding it to have a professional feel. For me, that means having a certain manner of dressing yourself (mine is a blue button down shirt and black blazer) that becomes part of your brand. It means having props and the means to carry them that show you are serious (bringing your props in a cardboard box doesn't cut it). It means having business cards, a website and a social media presence for your professional persona that are consistent with your brand. The idea of a brand is that people know what they are getting when they hire you. It is important that your brand distinguish you from the competition (for a reason other than price). The most important part of marketing is developing customers through word of mouth. The most important thing for developing word of mouth is that all your interactions with people be positive and professional. Treat everyone as if they are your most important customer and treat every show as if it is your most important show. There are a lot of threads about doing free shows. My sense is that when you are beginning you should do free shows if: 1) they are for a charity; 2) they give you significant exposure (50 or more people); 3) they know that you are doing it as business development and what your normal charge would be and 4) they are limited to 2 or 3 shows in total. Finally, don't market based on being the least expensive. If you have developed and rehearsed a quality show you should get paid a quality rate. Set a rate that you want to have long-term and start out giving a 20% discount. As time goes on, eliminate the discount (except for repeat clients).
Booking
Start off with a good system that you intend to use as your business ramps up. Make sure you have a way to follow up with people you've done shows for. That helps with repeat bookings and referrals.
Performing
This is where it all comes together. The most important thing is to keep it professional from the lead-up to the show to the follow-up afterwards. Be professional in all your dealings with your customer including accepting the booking, providing a clear set of requirements (if you need a table, if you want a certain set-up for the room, etc.) and following up a couple of days before to confirm the details. Arrive early so you can set-up leisurely (and don't be surprised if people want to talk to you when you are setting up). Start on time. Perform just as you rehearsed. Give it your best, don't just go through the motions. Recognize that your next customer may be in the audience. Collect the check and then follow-up with a handwritten note mailed to the customer. After each show, write down notes of what went right and what didn't. Make changes as needed.
I think your next step is to come up with some SMART goals focused on becoming a professional. I'd start with effects and presentations and work them into a show. As you start rehearsing the show, begin to develop what you need for marketing and booking. When the show is performance ready, then begin your marketing -- the bookings and performance will soon follow. Feel free to list your goals here and to update the thread as you progress.