Start and finish soft
In any training always start at a very smooth pace, and go increasing the intensity throughout it.
To finish the training, try to do at the end of it a few minutes of soft exercise of the sport you are doing.
Do not forget about warm-up and stretching
It is very important that you spend time in each workout to warm up and stretch, so you can prevent injuries and also doing stretching exercises, you can run, and swim better.
The technique, a fundamental part of training
Dedicate part of your training to practicing running technique, swimming, cycling, even if it does not seem like practicing this type of exercise, you will improve your efficiency in each sport and thus you can obtain better results and with the same effort run and swim faster, avoid injuries , etc.
Pay attention to your body
Sometimes training, work, and the social circumstances around you influence your performance, and can make you feel tired, unmotivated, etc.
In these cases, it is important to pay attention to your body, and if it asks for rest, give it to them. Nothing happens to lose a day of training, it is even beneficial in some cases.
Don't try to make up for lost training
If you have never been able to do a training session, do not try to recover it by doing double the next day, let it pass, do the planned training and do not think about it anymore, you will not lose your fitness.