Two "tricks" that worked for me (back in the days of bear-skin singlets and stone mats).
1. To develop your stance - when you are watching television and the commercials come on, get into your stance. Maintain the stance until the show starts again. Then you can sit down. This will either give you legs capable of maintaining a good stance throughout the match, or get you to give up TV. Both are worthy goals.
2. You can "slow down" the quick opponents by timing your shot correctly. Circle, and be aware of their feet. Just at the moment your opponent's foot touches the ground, launch your attack. It takes them a split second to shift their weight to move the foot. That split second will make a world of difference.