Assuming you are right handed:
- Make sure the end is cut square
- Insert into open port of the reel center with right hand
- Hold the film in place with your left index finger
- Start winding the film holding the film bu its edged with your right hand but turning the wheel with your left hand, finger still on the center
- Once the film as a turn on it, you can release your left finger and keep turning the reel with your left hand while feeding the film with your right
- I periodically stop turning the reel and push the film in very slightly with my right hand while now gently rocking the reel with my left. This ensures the film feeds squarely onto the reel as you go.
This sounds far more complicated than it is. Get an old roll of film you're not going to shoot and practice in the light until you get it right, and then work on it in the dark.
The old reels never had a clip at all, so this isn't some magic I invented. it's how I learned to load film back when dinosaurs roamed the earth.
I have a strong preference for Nikor SS reels because they have the best wind spacing of any reel I've used AND have the minimal amount of contact with the film. This promotes maximum fluid flow and evenness of agitation across the film surface. This is somewhat of an issue for normal agitation, but it is a Really Big Deal (tm) for low agitation/long duration development like Semistand or EMA. I tend to do a fair bit of this and have never had any issues with the Nikor reels. (The plastic reels with high wind walls are a nightmare of bromide drag and yuck if you try doing this with them.)