Listen to as much ska as possible. Search your local record stores and online for as many different ska bands that you can find. These should span all eras of the genre going back to early Jamaican ska to the newer bands on the cutting edge of the genre.
Determine your influences. Pick two to four bands that really stand out to you. Listen to their songs carefully for every part of the music. Try to notice the similarities between songs, and what musical motifs stand out for these bands as opposed to other ska bands.
Pick an instrument and learn the songs of your influences. Sheet music, guitar tabs and lessons on music theory are readily available online. You're ready to move on once you reach a point where you can figure out how to play these songs just by listening to them. This step requires lots of practice.
Develop your own personal style. Now that you have a strong foundation in the style of your influences you should create your own style. Create distinct music with your chosen instrument.
Find a band. There are many ways to meet like-minded musicians. Visit communities online. Hang out in record/instrument stores, and most importantly you should go to shows in your area. Once you find people, get together and jam.
Once you have a full band and some well-written songs that are polished, play shows. Don't expect immediate success. You have to stick with it. Use online resources to stay in touch with fans. Once you have a solid fan base you can get the attention of the movers and shakers in the music industry.