Ron Clifton's tips are a good base, as Rags mentioned.

What I can hint at is the ominous "ring finger lead" - try to "steer" your downswing AND follow-through with the ring finger. Make it a smooth, continous movement, no hurry, and watch out that the armpit stays closed (no wheeling around your hip) and your upper body is upright, square to your target.

Try to experiment with your wrist position. "Cup and collapse", like Rags tells, can work, but other options should be tried, too, since every bowler is different. For, me e. g., keeping the wrist locked throughout the swing works best.

To create some powerful roll, also try to hold your hand/wrist a way that lower arm and pinky build a "line", ring and middle finger should point forward and the index finger be angled away from this thought line. Spreading the index finger will improve back end reaction, too, as will a pinky placed tight to the ring finger (see Ron Clifton's tips - it works!).

This might not create a consistent release, but give you more roll and probably a more effective ball.

Also consider a wrist device (if you do not use one already). An inconsistent release can be the result of a weak wrist, coming around the ball (even if it feels different!) and cretaing more of spin than roll.
Also, check if you bow your upper body upon release. This is also a great source for errors and mostly the result of a too small knee bend. Try to keep your body upright upon release, it increases leverage and therefore ball reaction.

Video tape yourself and anylyze your shots. It is very revealing in many aspects and will surely help improving your overall game.

Hope this helps? Good luck!
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DizzyFugu --- Reporting from Germany
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"All that we see or seem, is but a dream within a dream..." - Edgar Allen Poe