Learn how to really swim. Learn weight positioning at your pecs and shoulder blades with a strong core so your weight does not shift to your hips. Exhale underwater. Your head is a rudder. The other rudder is your hand and arm. Breathe every other stroke. Throw before you row. Maintain your hand and arm in front of your body like your life depended on it until the other hand and arm returns to the front. Swim with your arms wide like you are getting out of the pool using the deck. Whatever your want your face to do in the water, have your palm do first. Swim your size. Big swimmers can do with fewer strokes and slower strokes while smaller swimmers do with more strokes and faster strokes. You might as well hire a swim coach. While I'm in Atlanta, I do travel. Contact me.
Learn how to be tireless on the bike. Keep the riding as simple as possible. Get on and off the bike cleanly. While on the bike try to keep the effort, the watts, the same whether going up a hill, down or on the flats. Work with a watts meter in training to understand the concept. This would also be similar to using a heart rate monitor; but, it is different in that your heart could be racing while your riding is inefficient. Get out of the wind. When going over 15 mph you are in a significant enough wind to be on the tri-bars or down bars. When out of the wind, like when you are going up a hill at 10 mph, you might as well be sitting straight up so you can breathe more openly and engage your leg and back muscles differently. Be a minimalist on the bike. Spend more money on lighter shoes and wheels (moving weight) before you do non-moving weight. Take off the second bottle carrier if you don't ride more than an hour during your triathlon. And there is more.
Keep your focus down the road while running. You don't want to dwell on how you are feeling. You don't want to feel the effort in your legs. Focus on your hands in front of you. Your chest and where in front you that chest is going to be in the next moment. Think of a fast and agile count like 123,123,123. Look down the road and not at your feet. Get your coordination (technique) going in a relaxed way and then increase the tempo. Put in miles and miles of training because you need to develop the arterioles to go with the sufficient muscle that you already have. I have yet to meet the person who has lacked the muscle. Everyone that I have met who is a poor distance runner has not developed a sufficient arteriole network in the muscle. You have to have the arterioles there so the muscle gets oxygen and food energy to the muscle at the cellular level. The basic arteriole development that you begin with is never enough. You must force arteriole development by keeping the blood pressure up while training and then the arteriole "roots" will grow. And as you are growing those arterioles, then you have more capacity to do speed work and gain agility to a greater effect. And this development also occurs in swimming and cycling. Your cycling muscles will get you about two-thirds of the way there running wise. Yet, you do have to run to get that last third.
Rest enough to go fast. While base training is productive and good, you will go at the same speed (albeit tirelessly) if you don't slow it down in order to speed it up. Try some fartlek running where you run as slow as you want and then as fast as you want to begin the development of your faster pace.
Use weights for muscle balance and then strength gain. Use resistance stretching to stretch the deadness and soreness out of your legs.
Train daily. Six days of the week at a minimum.
Don't let anyone less disciplined than you talk you out of what you want to do.