Usually you won't find much in the way of guides. I found the best way when I was learning was to watch some other recorded runs (don't go for WR runs as they'll likely use tricks you won't be able to pull off initially) and practice offline.
Once you're happy you can finish a run, regardless of the quality, start streaming - both practice and attempts (but continue practicing offline). You'll find that runners of the game will often pop in as they tend to follow their own games on Twitch, and offer you advice.
Join
https://forum.speeddemosarchive.com/ and post in the respective game you're learning, see if there's any discussion for routes and don't be afraid to ask for help. Speedrunners are always happy to see new people join and will often provide you with as much advice as you need.