As a Martial Artist I have always been asked where to begin, what style is best and a plethora of other questions.
I realize it can be intimidating, by watching movies to YouTube there is a menagerie of styles and "Opinions" of what actually works best. Along with those experts come the inevitable demonstration showing just how easy it is to disarm someone, or of course crush them like a bug. These experts continue down in my opinion what is a dangerous dream of what it is actually like to have a street confrontation, most never have had. I trained at many different Martial Arts clubs and I can think of maybe one person in all those clubs who had ever been in a street fight, so how on earth would they really know what would work and what would not? Answer, they only have a theory, but they do have the tools to increase their odds of survival, which is why you are reading this, and looking into Martial Arts yourself.
I will say right off you should always do your best to avoid confrontation. I have hundreds of street fights under my belt, with that experience comes the realization that all but a couple were necessary, confrontations are easy to avoid for the most part.
Avoid eye contact, walk with purpose and simply ignore the chants. Try never to put yourself in a bad situation, stay in a lighted area if dark and of course stick where there are other people.
In the event something happens, do not expect help, odds are unless there is a Police Officer in the area nobody is coming to rescue you. I was in a bar room brawl once with quit literally the entire bar, despite things not going well for me, not a single person I was with, and they were all very well trained martial artists, came to my rescue. I survived simply by making sure my temples were covered as well as my throat. Always protect your critical areas, always.
Get a bright flashlight. We live in a great time when cheap blinding flashlights are available, even in the daylight one of these blasts of light can temporarily "Disable" an adversary allowing you to escape.
Situational awareness; Most people frequent the same area and route over and over again. You should take the time to make mental notes for escape routes as well as possible places someone may lurk in the shadows. This goes along with driving as well, be aware of having your window rolled down at a stop light or sign.
Be especially alert while shopping, many people are robbed/accosted while simply putting bags into their car! Take a minute, look around, if you have kids lock them inside the car before you unload your goods into the trunk.
Carry your keys so they protrude from either side of your middle finger, you can then punch someone and it will hurt like hell.
Imagine; Your Imagination is your best friend, and your worst enemy, for the sake of this article we will use it as your best friend. It is good if you Imagine horrible things happening, now imagine how you will get out of those horrible things.
I am someone nobody should ever watch a horror movie with, the entire movie all I can say is "Why did they not do this,. or this etc." this Is a lifetime of training myself to not only think differently from other people, but to imagine a way out of the worst possible scenario.
Strikes; In the event of a self defense situation you are not looking to "Bang it out" with the bad guy, you are looking to hopefully finish them quickly or to buy yourself some time to escape. Aim for the eyes, be it gouging or poking do not play fair, and do not quit, the eyes are painful as hell to have poked or gouged. Chop or punch to the throat and do not stop punching or chopping you always want to overwhelm your opponent. Go for the groin, kick punch an even grab and yank those toodles, the last will stop anyone right in their tracks as if they are a cartoon character. Stomp on their feet do anything you can think of to make that escape. If need be bite, scratch pull hair, pull ears. Fight as if it is your last breath, if it comes to this situation, it possibly could be.
Get a firearm, a concealed carry permit and get proper instruction on using it. This instruction goes well beyond the basic CCW one day classes, spend the extra money on an actual self defense/combat pistol class. Do not let the weapon simply collect dust in the closet after shooting it once, make a conscious effort ot go to the range several times a year. The more often you use the weapon, the more confident you will be if you ever do have to use it. Muscle memory is paramount be it hand to hand or using a weapon.
This leaves us with what art to actually take. While if you are in good shape a MMA class is arguably the best, the reality is you have a life to live and do not have the time, or energy to devote to a high intensity class, further you may not be a pillar of fitness yourself, so be realistic about your choice. While some styles are clearly better than others, go with whatever is closest, convenient and comfortable for you. Go ahead and meet the instructors, most places offer a free class, take it.
Anything is better than nothing, you will at least learn how to throw a punch or a kick so that puts you a huge step up over the average street thug. Keep in mind police only take a few hours of grappling and they can handle the bulk of street thugs, if you take a class often you will be way above that.
Most arts will offer a self defense class, I encourage you to take that class, while not everything they teach will be good, most of what they will teach you will help you out, especially in scenario presentation. Further it gives you confidence, and confidence is something people can read in body language.
Just like with firearms, the more you train the more confident you are. I would also like to say that a female friend, whom by her own admission is not athletic at all, has enrolled in Karate over the past few years with her daughter. The one thing she has gotten out of her Karate from sparring is the realization that unlike the movies, she was not going to curl up in a ball and cry when she actually did get hit in the face. She is now ready to test for her brown belt!
My step sister has kidney problems, she went from being on the verge of Dialysis to competing in Brazilian Jiu Jitsu. While she no longer competes, she still trains and loves it, she is also someone whom previously would not have been known for any athletic ability at all. I am beyond proud of them both.
In the end, remember what is between your ears is your absolute best weapon you can possibly use, always always keep your head.