My advice will be to go find a school and train with an open mind. You will not need conditioning for a long time, and much of what we do does not require much other than endurance - particularly the sport-oriented schools.
For these schools, it is typical to spar a lot, do high fancy jump kicks, break boards, and compete. Here, strength, endurance, flexibility, and conditioning will occur naturally throughout your progress.
For other schools, strength and flexibility is less important, and they focus on hard-core self-defense reguarless of your physique.
Every school is different. A good instructor will explain everything to you and allow you to train at your own progress and as well as encourage you to try harder. That, mixed with some reasonable practice at home, is all you need. Whether taekwondo, mma, or anything else.
Just... find a good instructor. That is key above all else.
If you are serous about training for Taekwondo, you may find the conditioning different. First to increase your flexibility you will be doing stretches. To increase your flexibility, you need to stretch both outside and inside of class as well. Cardio can be improved any way you want to( running, swiming, jogging, etc.) Your strength can be improved the same way.
I will say this, if you take traditional Taekwondo, you will spend allot of time working on your technique. Technique is vital. Technique teaches how to use your body for maximum damage.
You will be what you train to be. Simply all training is task specific. For hardening the forearms we do blocking drills at increasing force over time to develop them to be able to block without much pain or bruising. The same with shins and thighs. Light sparring without gear except of course head, mouth, and jaw protection. This will develop your midsection. I emphasize light sparring! don't injure yourself as this only sets you back. A good instructor with experience can lead you through this process. It takes time and lots of practice. Flexibility from stretching. Use static and balistic. Otherwise strength training is the same for everyone even martial artist. LOL Please get help with this from a pro.
Body conditioning, flexibility, speed, strength, etc... All due to training efforts. Pain tolerance came from adrenaline and endurance training (punched on belly during sit ups, etc.). Some said it's because of your muscle mass. But of course you'll get more pain tolerance after some fights. It'll improve itself.
I was practicing TKD until I get bored and KO-ed by a MuayThai fighter. Then I chose MuayThai and some other martial arts just for experience. So I think I don't wanna suggest you to do TKD unless you wanna use it only for body fitness and flexibility training. But not for fighting. Sorry.
My first question involves a long, convoluted story about me previously hating Taekwondo and now wanting to try it. Any advice on starting TKD/training it in general? My second and more important question is, how do you guys condition your bodies? How do you build pain tolerance in the stomach and facial area (aside from the obvious, sparring)? How do you improve your strength, speed, and cardio? What about flexibility?