You will need a lot of flexibility if you want to increase your accuracy. Bear in mind that you can always bleed off speed, but you can never gain it back.
In order to increase your "wiggle room", I recommend doing a retro burn farther away from the base than is orthodox. When you are at about 70 km or so, adjust your flight pattern in such a way that you gently glide in the upper atmosphere, holding your altitude relatively level. Use your speedbrakes if you think you are coming up too fast, but don't lose too much speed.
In order to increase your "wiggle room", I recommend doing a retro burn farther away from the base than is orthodox. When you are at about 70 km or so, adjust your flight pattern in such a way that you gently glide in the upper atmosphere, holding your altitude relatively level. Use your speedbrakes if you think you are coming up too fast, but don't lose too much speed.