In the Dragon Ball series, characters have had their own special abilities/techniques. For example, the Instant Transmission. During the Buu saga, Cell saga and tournaments etc characters such as Piccolo or Vegeta may have needed to use such techniques. Also, the fighters are so fond of getting stronger. So why is it that the characters do not teach each other moves that may be extremely helpful in battle and never seem to change their set of techniques?
This isn't necessarily the case. It depends heavily on the personalities of the characters using the technique and the character who wants to learn the technique.
- Krillin wanted to learn the Kaioken at the time Goku first revealed it. Although, he never followed through.
- Vegeta is too prideful to have Goku teach him how to use instant transmission or any technique for that matter. However, if you recall, after Namek, the latter was in search of Goku to ask him how he managed to turn into a Super Saiyan. It would be against Vegeta's character to ask Goku to teach him very simple techniques when Vegeta himself is a battle prodigy and could figure them out or come up with variants himself. That didn't stop him from asking Whis to train him as the Vegeta clearly knew how strong Beerus was and the former's teacher would be very experienced and significantly more powerful.
- Goku on the other hand, despite having the power of a God in Dragon Ball Super, still goes to Master Roshi to learn the Mafuba. He later adopts a technique he watches Krillin use in his fight against Jiren. His character has been written in such a way.
In conclusion, it simply comes down to fighter's particular character. That said, the only convenient technique Goku has which the other fighters could find useful is instant transmission. Not to use during battle as it can be easily countered "We watch Frieza easily counter the Yardrat using Instant Transmission in the tournament effortlessly". It could be convenient for travel. The show has kind of adapted the attack as one of Goku's signature attack for the sake of plot convenience. That said, Goku says it took him 1 year to perfect instant transmission. It makes sense for Goku to have spent a year to master the technique based on the circumstances he was in at that point in time. Goku is also superior to the rest of the Z fighters as far as the technical aspects of Combat is concerned(Disregarding Whis and maybe Beerus of course, if you consider them to be a part of the crew). So it doesn't really make sense for the rest of them, to spend a year or possibly much longer, to master a technique simply for the sake of travel.