Speedrun games you really like/have a lot of knowledge about. It's also best to start off with games that aren't too long. i.e. don't start with RPGs like Final Fantasy. Also practice. A lot of practice.

Also if we're discussing Speedrunning, we should also bring up TASes as well. For people who don't know what a TAS is, it stands for Tool Assisted Speedrun/Superplay. It's when you go into an emulator and slow a game down frame by frame to get the most optimal time in a game. Most of the time the end result is some of the most ridiculous gameplay you will ever witness.

I'll use F-Zero GX as an example, since I follow/participate in speedrunning in that game. I'll post the Maxspeed WR, and I'll post the TAS version of the same track.





Anyways I speedrun F-Zero GX. Most of my times are pretty decent (a couple of them are within a couple seconds of WR. By F-Zero GX standards, that's somewhat impressive. Most people are usually within 10-20 seconds off WR on some tracks (sometimes longer). At some point, I'll make a spreadsheet of my times, as well as a brief description of the advanced techniques used... and there are A LOT of them. I don't have a capture card, so I can't really record my runs unless you want to see shitty phone quality video.

I also follow Ocarina of Time speedruns, since they're pretty neat to watch (mainly 100%) and Majoras Mask (any%)