Naturally, if you want to be able to bet on a sport, you have to be familiar with all it's aspects. To my knowledge, no other sport has athletes competing against each other using such vastly different methods and techniques. That's why it's crucial that you study each art and analyze its strengths and weaknesses.
The martial arts of the UFC can be broken down into 2 main categories: striking and grappling. A fighter will either try to knock their opponent out or force them into submission.
Karate (Shotokan, Kyokushin, Kenpo)Karate is a Japanese term meaning "empty hand." Essentially, many techniques fall under this category, but the Ones most seen in UFC fights are Kyokushin, Shotokan and Kenpo. Karate is base purely on quick, accurate and powerful strikes using both legs and hands. One thing that should be noted about karate practitioners is their ability to focus, even when being charged, and deliver knockout punches. Chuck Lidell is a great example of this; many times he can get his knockouts while backing out of a flurry of his opponent’s strikes. The lesson to take from this: never underestimate karate’s defense against both rushed striking and grappling clinches.
Boxing is a stand up art focused purely on punching. Needless to say, boxers carry devastating punches. They also focus on their footwork and upper body motion which gives them an edge on dodging punches and high kicks. Where they tend to lack experience is in ground work and low kicks. Their emphasis on the upper body might have them forget about the low kicks, making their legs easy to weaken. A boxer with beaten up legs entering a grapple has his odds severely reduced. However, the odds of seeing a MMA fighter with only a boxing background are slim to none unless you're watching a UFC in the single digits. Nowadays, boxers will round themselves out with a grappling art like wrestling or BJJ. Still, even with the grappling, boxers have trouble against legs. Example: Quinton "Rampage" Jackson, fmr. UFC heavyweight champ with a boxing/wrestling background, has been KO'd and TKO'd exclusively by kicks and knees.
Developed in Korea, Taekwondo is all about kicks. Literally, the name "Taekwondo" translates to "the foot and fist strike art", however kicks dominate the art. In a moment's notice, a TKD artist can deliver a knockout kick straight to the head. Fighters who go mad punching and rarely work on their dodges and dips run the risk of being floored by any number of TKD kicks. Like boxing, I can't think of any fighter who solely relies on TKD for their experience. A TKD fighter will usually have a grappling art under his belt as well (eg. Anderson Silva). Mostly what a TKD experience should tell you is that you can give "kicking proficiency" a big check plus plus on the fighter's profile. When it comes to range, TKD wins hands down. Not only does it emphasize the use of the legs as its primary weapon, but TKD also stresses mobile kicks. To achieve greater range, fighters will move forward as they kick in order to achieve the maximum possible reach advantage. (see video below)
Muay Thai (or Thai Boxing)
Muay Thai is Thailand's kickboxing. Whereas regular kickboxing consist of punches and kicks, MT throws elbows and knees into the mix. Why? 'Cause the Thai are just that much more badass. Knees and elbows are dangerous for two reasons. Firstly, they direct a tremendous amount of force into a relatively small area on the the body, causing devastating damage. Secondly, they allow the fighter, who's already dangerous at long range, to be dangerous at close range and clinch attempts. A grappler who's too slow on his clinch will find himself barraged with a MT expert's knees aimed directly at his face.
Kickboxing, I assume, needs little explanation. Basically, it's boxing with kicks thrown into the mix. The result is a fighter who will wear his opponent down with lightning fists then, without notice, deliver a wrecking ball of a kick to the temple. Despite the fact that kickboxing consists of both punches and kicks, it crucial to realize that the majority of KB fighters will favor their legs knockout. Legs have both longer reach and, since they've perfected the accuracy of their kicks, a tibia whipped at an opponents temple will almost always result in a KO. This gives them an edge over fighters using a shorter range technique like boxing.
Brazilian Jiu Jitsu (BJJ)
The UFC you know and love was made by the Gracie family purely to show the world that Brazilian Jiu Jitsu kicks the shit out of any other martial art. It just so happens that it did exactly that. For the first few UFCs, BJJ dominated all other fighting styles. Just to show that it wasn't brute force and was actually a flawless technique that was conquering UFC belts, the Gracie family elected that Royce Gracie be the one to fight instead of the older and larger brothers. The logic that if Royce, who was flirting with 180 lbs, could submit any fighter that stepped into the ring with him, then there must be something to this BJJ.
As for the technical side, BJJ is a grappling sport based on gaining a dominant position and, from that position, have the dominant fighter utilize his largest muscle groups, along with his body weight, to exploit the smallest, weakest joints on the opponent and extend them past their normal range of motion to the point that the pain becomes intolerable. The reason this was so successful was that, all the other martial artists that had fought Royce had never before been in such a scenario where they're on their backs on the ground, especially not the boxer (see UFC 1 vid).
Whereas with other martial arts I mentioned that fighters would combine another martial art to get some sort of balance, you will occasionally see fighters coming in with a background heavily saturated in BJJ.
Wrestling (and Greco-Roman Wrestling)
Wrestlers in the UFC have one goal: to slam their opponent on the mat....hard. Wrestlers have the amazing ability to rob their enemy of a center of gravity and bring them down hard. From this point they'll either attempt to submit or, more likely, ground and pound away until either the opponent or ref decides that enough is enough. Ground and pound, you have to realize, is much more dangerous than standing punches. (watch this video).
While the video goes over all the essential benefits of ground and pound, one point that I see as misleading is when they state that G&P seldom leads to a knockout. You can't say that each of Couture's punches are double that of a heavyweight boxer then, in the next sentence, that it seldom leads to a knockout because of "turtling up." Take into consideration that:
a) The opponent cannot move back
b) The fighter's strikes are aided by gravity/body weight
c) The opponent's counterstrikes are weakened by gravity
d) The oppenent's body is absorbing much more shock from the strike since the ground is preventing recoil
The truth of the matter is that ground and pound is lethal and the only reason an announcer would make such a statement is to (poorly) segway into the next topic.
Judo is meant to be a soft and gentle art. Practitioners (judoka) learn to use the momentum of their opponent against them. It's from judo that sambo, aikido and Brazilian jiu jitsu originated. Judoka have their way of removing their opponents' supporting leg then, when the weight shifts, topple them onto the mat for an unforgiving joint lock. While there are strikes in judo, they're not directed at a knockout; rather, to facilitate an inevitable takedown.
An anagram for "self defence without weapons", the Russian Sambo was originally designed as a military self-defence technique. Only later did it become a sport. It includes the fierce strikes of karate, the unbearable submissions of judo and the devastating slams of wreslting. It shouldn't surprise you to see a fighter using a purely sambo background since it is, in itself, a complete MMA fighting style. Weaknesses in sambo practitioners vary from fighter to fighter since, in theory, their style encorporates all factions of UFC fighting. One of the most famous fighters using sambo is Fedor Emilianenko. You won't be seeing him in the UFC, but that's politics I won't get into.
Other arts that are popular but just aren't suited for UFC, for various reasons, include (but aren't limited to):
Aikido, savate, sumo and capoeira
So there you have it, a BRIEF intro to the main martial arts you'll be seeing in the UFC. I stress that these descriptions are neither complete nor is the list exhaustive. If you have any arts you feel are worth mentioning, comment below and I'll add to the list.