So here’s how I make gifs.
Download the MP4 for the video. I got the 1280x720, because honestly, why do you need it so huge anyway? Nobody will be able to watch it without lagging :P
File>Import>Video Frames to Layers…
Pick Selected Range Only, so it won’t try and turn the entire video into frames, which could potentially cause your computer to run out of memory and crash it. Then hold shift and select the range you want.
Results in this. Okay, say I want a Donghae gif. I cut the Hyuk parts out (sorry bb) and end up with 7 frames of HQ Hae sexiness.
If it’s an HQ gif, usually 7-10 frames is the maximum you can have for a gif under 500kb without massively deteriorating the coloring. So this is perfect.
Fix the frame delay rate (it’s 0.14 seconds here).
Go to File>Save for Web & Devices, and here is the screen where you fiddle around with the color/dither settings until you can get under 500kb (assuming you’re using for tumblr. If not, then don’t even worry about it.)
Hope that helped.