You have to get past the notion that the holes are there from the outset; if you are fighting a good fighter or even an average one they should be out of range or able to defend a first shot and maybe a second, and a third (and so on). You have to make a fighter act or react, usually more than once, before an opening develops.

Establish a pattern with your jab or a 1-2 and then break it, change levels, punch a glove a shoulder or an elbow, alter your angle by moving your feet and your torso. Most importantly put punches together. Make sure you develop some dependable counters. Openings are almost always created when your opponent punches.

For instance you may double jab to close the gap and get in range, throw a 2 that will likely be blocked come back with a left hook to the head, he raises his glove slightly to catch the hook and you cut it short, pull it back and land the left hook to the body, maybe he even gets that one with the elbow but you drive a right upper cut through the hole created by the hook to the body.

Boxing is like music in that the discordant note can be very displeasing.