Spar as much as possible. The more skilled your partner the better. If they're not that good go easy on them n try out new things like different combinations or avoiding punches with head movement. I've seen people do boxing for years but not spar that much and they're the same level as people who have boxed for less years, but done a lot of sparing
Train hard, know that you CAN be the next mike Tyson or Muhammad Ali, or rocky marciano, use motivational speeches, constantly meditate on your goal to he a badass boxer, use your inner strength, use your primal side to get through you're training, use proper nutrition, you tube search for motivational speeches, YOU CAN BE THE NEXT MUHAMMAD ALI,
You train. That's all their is to it. Any real boxer would tell you that. There ain't no magic to it. You train hard and work for it.