First and foremost, make sure you are "anchoring". The most common anchor point is the tip of the middle finger firmly tucked in the corner of the mouth, using the "split-finger" draw (one over/two under the arrow). Now you're sure the arrow is at least LEAVING from the same point every shot. And, KEEP BOTH EYES OPEN!
The quick answer to your problem is to start closer than you are already shooting. Called the "step-back" method, start at about 5 yards. First just be concerned with "grouping" your shots. They don't have to be in the bullseye to start. If you can hit within a 4" - 6" group consistently, Then concentrate on MOVING THE GROUP into the bullseye. Once your groups are consistently to center, move back a yard. Repeat this process all the way out to 30 yards - which is beyond the 20 yard "ethical" traditional shot. This yard-by-yard step-back approach is the best method to learn true instinctive shooting.
If you just can't do that, then you must try the "reference point" method. You need a big target for this. Start at about 7 yards and put a sticker about 18" below the bullseye. At full draw, close your left eye (if you're a righty), and - properly anchored - sight the tip of the arrow on the sticker. Shoot a volley of 4 - 6 arrows. They should all hit the same place on the target - bullseye does not matter. (Obviously, if you miss the target totally, then you must place the sticker at another starting spot.) If your shots do not hit the same spot, then you are NOT steady with your aim. With good luck you'll smash an arrow when you get the hang of this.
Now, measure the distance & angle of your "group" to the bullseye and move the sticker the same distance and angle to bring your shots to center. Once you have the hang of this, you should be able to use this method at any distance. The idea of this is to give your mind the picture of where the "sweet spot" is in relation to your bow hand. Once that "picture" is in your mind, you must STOP this method immediately and start shooting with both eyes open again. DO NOT rely on this as a method to be used in the field. It is only an exercise to bring your hand/eye coordination to center.
Last and least is "gap shooting". Many archers use this method whether or not they realize it. It is a variation of reference shooting, but requires a long outdoor range. Remembering the importance of anchoring, simply start at about 40 yards and again, sight the tip of the arrow this time RIGHT ON THE BULLSEYE. Be prepared to totally miss the target until you find the range at which this works. The distance it works at is totally up to the draw weight of your bow. Once you find the distance at which your arrows hit the bullseye consistently when you sight the point on the center, then open the other eye to bring in your depth perception. Your dominant eye (hopefully your right eye if you're a righty) will still do the aiming, but it's important to use your full depth perception granted by the use of both eyes.
Practice long and hard at this distance, whatever it is, until you are steady in the center. The key goal is consistancy.
This method inherently forces you to get your dominant eye right over the arrow, eliminating windage deviance.
Once you "have it down", move 5 yards closer and adjust the point of the arrow respectively lower to compensate. 5-yard increments are perfect for this method. More creates difficulty, and less is not enough to see variation in aim point effectively. To practice longer shots, obviously place your arrow tip above the bullseye. Stay at each change in distance until you are (you guessed it) CONSISTENT!
These are the best methods to experiment with. I like to push for "true instinctive" shooting with the "step-back" method. One of the above methods WILL work for you.