Seoinage is certainly not my tokuiwaza (best, favorite throw), but here is a handful of good pointers that I work on to try to get better...
- Make sure that when you turn in, your knees are well bent, placing your center way under theirs. You will often want to make sure your feet are closer than hip-width apart and between his feet. Watch the efficiency of the master’s footwork in the first video above.
- To make a good time to enter, bump uke when he puts a foot down then use the recoil off the bump to turn in. Watch the bump and turn-in on the second video above.
- You might try thinking about that bump as pushing yourself backward off of uke, as if to disengage. Then, when uke does not allow you to disengage (that is an attack on his part), turn in and throw. You just tricked him into attacking you so that your throw is easier.
- Try the same trick from an outside cross grip, as if uke reached for a grip and tori executed aikido release #1 or #3, ending up holding the near arm down and out and holding the back collar with the other hand. From here, bump and turn in.
- Uke, if you can slide around this entry and crush tori onto his hands and knees you will be set for koshijime (A.K.A. clock choke), among other things.