NGHL is hands down the best version/build of the game to use when it comes to speedrunning in general, however you might choose to use other versions for different reasons, sometimes certain goals require the use of WON or Steam versions.
I’d also recommend downloading Bunnymod Pro if you’re looking to speedrun HL1 or jump maps, it’ll help you improve your skill a lot quicker due to the various different features and indicators available, for example there’s a timer to practice damage boosting with hand grenades.
That tutorial that OMalley linked seems pretty good. You should head here for more information on getting started, there’s also tutorials on movement including bunnyhop for GoldSRC (as opposed to Source, which is what that tutorial is done in). I actually thought about creating some short video tutorials for each different trick in Half-Life/GoldSRC as I’ve noticed that there seems to be a rise in popularity for GoldSRC running as of late, but there doesn’t seem to be much in the way of visual demonstrations outside of the CS KZ/jumping community. It’s still something that I’m considering doing, but I also have to consider that I have a lot of other projects going on at the moment.
If you’re using a bhop script but you’re not using NGHL, you should check to see what your fps_max value is in console, since this can affect the consistency. Fortunately NGHL comes with a decent bunnyhop script and it’s configured to run in 250fps by default, so there isn’t usually a problem.
Thanks to consistent scripts, nowadays bhop isn’t too hard to learn. I remember back in the day when my friend had just learned about ‘this new bunny jump trick thing’ and the best script available was one that spammed 2 jumps instead of 1, we’d spend hours trying to exceed 500+ units in crossfire thinking we’d got the hang of it, I wish I could of seen how I would of reacted to HL21 back then, lol.