Kihon or "the basics" are the foundation of all kata movements. All too often the karate student wants to learn as many katas as possible before they become proficient in the basic karate movements. A similar analogy would be for a man to want to collect as many weapons as possible but does not how to use any of them well. One man with only one weapon that he has mastered will easily overcome the person will all the weapons and little proficiency as to how to use them. Without proper form in the basic movements (stances, punches, blocks, kicks) the kata will lack power, focus, and balance.
Therefore to make your kata better, concentrate on the kihon first. For this reason kihon practice is an integral part of karate training no matter the level of the karateka. Kihon training never ceases. The most basic movement such as the punch can always be improved on. The karate student needs only observe an advanced student doing basics to see the difference. If you watch the advanced student do the same basic move versus a master you will see even more difference. In karate, the training never ends and is a lifelong endeavor that never ceases to improve.
Break The Kata Down
Learn the kata in sets and practice the sets individually many times repeatedly. Within each set of movements, each individual movement, their link to one another, and the transition to the next movement can only be mastered through practice. By breaking the kata down you are able to focus on a piece of the kata at a time and give it your complete concentration and self-evaluation to each set. Practicing the entire kata from start to finish 100 times is not near as productive as practicing each set 25 times each by itself and the entire kata 25 more times. Improving the pieces by concentrating a set at a time is they way to make the entire kata better and is a more efficient use of training time.