Keep working toward the lowest score you can achieve. Do stroke drills regularly. Stroke drills both diagnose and correct your stroke errors, and can be used for conditioning as well, which is why most Olympic swimmers devote at least 10 to 20 percent of their total yardage to them. The less polished your stroke, the more you should do. On each 75, do right arm only on the first length, left arm on the second length, both arms on the third.
Count strokes each length.
Get a coach. Practice helps a lot, but there's no substitute for a coach's trained eye in correcting poor technique. If you don't swim in a coached Masters program, the most cost-effective alternative is to attend a stroke camp or clinic. Have your strokes videotaped. Most of us learn faster with our eyes than any other way.