Every year several masquerade ("mas") bands present the theme for the coming year to which their band's costumes will relate through the design and colour(s). The idea is to be original every year, every band, every section, while still staying on theme. The official party in which the costumes are presented to the general public to encourage people to join that band as a masquerader ("play mas" or "jump with" the band) is called a band launch. North American carnivals generally have band launches around two months before the carnival date...but not Trinidad. Trinidad bands launch as early as July of the year before the Carnival, and the largest most popular (and often most expensive) bands are among the first to launch (they have 2,000-5,000 custom made-to-order costumes to produce, so I am sure that is one reason why!).
Whatever costume you like the most, you wait until the band opens registration (or online registration if you're not in Trinidad) and pay the required deposit for them to begin making your costume. The more popular the band, the more likely that the most in-demand sections will sell out FAST. TRIBE is the most popular band (it recently split in two because it got so big, so now there is TRIBE and Bliss)...and their hottest costumes can sell out in DAYS of registration opening. HARTS is the next most popular band, and sells out almost silently! For example, they launched registration last week Thursday 8/19, and already sold out one section.
So if you want to get the costume you want, it pays to be ready to go with deposit in hand (or sent down to a friend IN Trinidad with your measurements and section choices to the band's mas camp) the FIRST day registration opens. If you are open to playing in 2nd, 3rd, maybe even 4th choice sections, then you can relax and let the cards fall where they may.
Aside from the costume are considerations about the band's reputation for quality and customer service. Check out their web presence and social media, their responsiveness on the web and on the phone, word of mouth (including bloggers but keep in mind this is only OPINION so check many sources!), and the ease of registration from afar if you don't live in Trinidad. You also need to think if you want all-inclusive (more expensive, they provide food and drinks, but if the band is managed sloppily, you may get sorry food or they may run out of food and drinks on you!) or non-all-inclusive (cheaper but you need to make sure if you're new to Trinidad you don't lose your band and end up stranded if they are on the move and you stop off by some vendor somewhere for food and drinks.
Despite the hype over certain bands, every band has several masqueraders who are with their friends or associates enjoying the vibes and making their experience what it is! Smaller bands tend to launch September or after but you have to know what you are doing with some of them or be playing mas with someone who does!