Uki-Otoshi is all about understanding Kuzushi (breaking balance). By stepping back and dropping to one knee you create a gap. Use your hands to pull uke into this gap.
How to throw with Uki-Otoshi
1. Take a step backwards and pull uke forwards and off balance.
2. Drop quickly to one knee to create a gap between you and your partner.
3. Uke will now fall into the gap you have created. Use your hands to direct the throw.