The techniques in the GP 150cc mode are much more numerous than in the T.T mode. We're going to classify all the different kind of techniques and their level of difficulty.
Basic techniques (B TECH) :
These are pretty much the same than in the TT mode (hopping in order to improve the driving line, especially in the turns ; jumping before hitting a wall in order not to lose all your speed ; getting a turbo start by pushing and holding the B button, between (almost halfway) the first and the second light ; ...) except that you're driving much much faster in GP 150cc mode, hence, some turn will be very hard to handle at full speed. Here you will have to anticipate almost all of your turns and use a lot your R/L buttons. You can also slide on the undeep water or the snow without losing too much speed, you just have to jump on the snow or the undeep water by holding a direction. This technique is a little harder but very useful on KB1 and VL1 for example.
Advanced techniques (A TECH) :
The advanced techniques mean actually the good and wise use of items.
This item is very useful if we want to cut some parts of a track. These parts will often be water, grass, sand, mud, or snow. The mushroom makes your speed rise for a short period of time, so if you use it just before hitting the water/grass/sand/snow/mud part, you won't be slowing down, even when coming back on the regular path of the track (one can say that you may go faster than usually).
This item will let you go on the grass/sand/snow/mud and the undeep water without being slowing down! This item is particularly useful on tracks as the VLs, the KBs and the CIs as it may also increase your speed a lot. Nevertheless, in the other tracks, the star may not make you driving at max speed! Of course with this item you're invincible,....but don't fall into the void, the deep water or the lava!!! Also, boosting, steering, skidding & sliding may be harder or almost impossible to do with this item!
This item makes you jump above everything : characters, shells, bananas, sand, grass, mud, snow, water, blocks, walls,... all kind of fences, and you can even jump over void in order to reach another part of the track!...
Very advanced techniques (A+ TECH) :
There are different kinds of A+ TECH :
The second kind concerns the very accurate use of items. Indeed, the correct use of items may make you earn some big time for your records. Some items are much more useful than others (and depending on the kind of track). Also, you can try to get a second item just after having triggered the first one, it's quite hard to make a benefit from it but it can be very useful & can help you to develop new strats (for example, you can try to get 2 successive feathers and achieve a very fast lap at KB2, by using the inner side of the track ;-). It wont be considered as a trick).
The use of mushroom can be done just before a yellow bouncing line or a soil bouncing line then you'll make a huge jump cutting enormous part of the track. The mushroom can also be used on water : if you trigger it just before hitting water and use the R/L buttons you'll be able to bounce a few time before sinking. The first bounce may be automatic. In NTSC and maybe in PAL, it's possible with a specific timing to get automatic multi-bouncing on the water (...).
The LB can be performed within strategies that can help you perform a shortcut more easily.
The LB can be performed with mini driver cheat in order to get the best times.
The use of feather allows players to jump above fences or equivalent. This item can sometimes make you cut half of the track!! You can also combine it with another technique for more usefulness.
Of course there are few other techniques like :
---> the "releasing gas" technique : which consists in releasing the accelerator during a short period of time, at the end of a MB or a mushroom, it will increase the effect of the MB or the mushroom, it will also make you cut more sand/mud/grass/snow or undeep water without being too much slown down. Just take care of holding back the accelerator button if you want not to lose speed when the "releasing gas" beneficial effect is ended. Then it is also wiser to perform releasing gas technique at the end of the last lap or at the end of a fast lap try.
---> other techniques like holding direction when doing a mushroom (it can increase the length of the mushroom effect, especially on the undeep water and maybe on the ice & snow too where it combines with the effect of the slide), taking bouncers in order to go over walls, and combining different techniques described on this page. If you make a MB and take the CI bouncers, the MB will last as long as you can take close bouncers.
---> new technique discovered : the infinite boost (IB) (link). The technique seems to make a MB then the MB works, release gas and take an arrow. You will have an IB. The boost will be infinite unless you press any other control button than the D-pad or you hit any fence. When you have got an IB you can press again the gas it won't kill the IB. If you hit a character, the IB will still be working but you don't have to jump in order to avoid the character, just let be hit and you will continue boosting. If you use Bowser/DK, the IB is dead when you hit a character (maybe because of their slow acceleration start). If you hit a jumpbar just after taking the arrow, the IB won't work.