A few things with the side kick rather than the round kick is that the side kick will keep your opponent at the end of that kick. Round kick are good but they can be walked right through or the opponent can go to your non kicking side and totally make you waste your energy. One thing about the side kick is that alot of people throw them incorrectly for sparring. Make sure you are throwing your hips into the kick not just to leg this will add stopping power. Easy fix is "shadowboxing", bag hitting, partner assiting and just plain out sparring. Lead round kicks are nice to set up your side kick because the chamber can be intergrated into both which means I can fake round (headhigh) then side kick ribs or vice versa. Just experiment man and have fun. Also, spar lightly so you can work on things and don't hesitate to tell your sparring partner to calm down the power if its too much because your training to learn not to fear your partner.
Be "Water" my friend!