Plenty of stuff on the Internet. Look up some of the SEALs such as Stew Smith - excellent workout library. He was a company officer at USNA and helped many a mid ramp up their stats. Keys are good form and technique, breathing, and doing basics on a regular, committed, schedule. I have logged more than 50 years on the planet, and before breakfast, I still do the 100 sit-ups in 2 minutes and 65 push-ups (good ones), plus stretching and a few other big-muscle basics, unless I am really sick. Only reason I can still knock out the sit-ups and push-ups is I have been doing them every day since my late teens. I do pull-ups, 10, 3 times a week. Hate them, but I know if I stop, I will lose ground rapidly, especially since I am female, and, sigh, getting a bit creakier. Building a strong core is important, so you can hold your body still and minimize movements that add inefficiencies. I do my regular workout later in the day, which is a mix of various cardio, strength-building, flexibility and balance routines, depending on the rotation. I credit the Navy with giving me the habit of lifelong exercise.
Just google Stew Smith sit-ups! I also have one of those bars that hook under a door to stick my feet under.
I think my real advice is, get a good routine, and don't stop maintaining a baseline.