Midian's site provides an explanation page about some techniques.
Archibald LEFEVRE's page provides some short videos, especially some normal shortcuts that can be achieved with items.
SMK Online provides some videos : some ones are only for fun but some other ones can help you for the GP150cc competition.
You can also check this page which offers links of Match Race videos (you must copy-paste the links in your browser).
Nevertheless, these videos may all have been done on an emulator (sometimes with save states), and some of the strats can be impossible or harder to do with the cartdrige ; also be careful that you have understood the rules and techniques pages before trying to do the same strats than in these videos. Please read carefully the rules & techniques pages before trying to do the same strats!
Drew Blumfield and El Nico provide loads of SMK files : check it here & here respectively !
El Nico also provides a page for some SMK stuff : check it here!
EXTRA 1 : Hue Le has made a video of a mushroom cup run in GP150cc where he can finish the cup at the 8th rank!
EXTRA 2 : Florent LECOANET has made a video which is a compilation of the best PAL videos available for all the 20 Fastest-lap times!
watch it on youtube!
EXTRA 3 : Florent LECOANET has made a video which is a compilation of the best PAL videos available for the Long Boost technique, performed with arrows!
watch it on youtube!
EXTRA 4 : Tricks & Shortcuts video.
watch it on youtube!
You can also check the NTSC videos.