What are ways for a SPC to develop into a good SGT?

If you don't have the skills, get knee pads lol.

Just noticed your mos , volunteer for medical duties, teach CLS if given the opportunity.

If you are army, do correspondence courses and ask for more responsibility, ie. Leading PT, teaching classes, etc. Take initiative and keep up on warrior tasks.

Always be opened to learning new things. Don't get complacent, There's a reason we have the NCO creed (Follow it). Like my leaders have always told me think 2 ranks ahead. So although you're working on making SGT, go beyond and start looking at SSG as well.

First, meet or exceed the requirements. Second, observe your leaders and learn from them. Remember that some seniors are not the best to emulate but learn from that. DO NO SHARE A NEGATIVE OPINION! Keep it to your self. Set realistic goals. Finally, don't be discouraged by the Military. The Military is what it is. It's the people that screw it up.

SPC Joy - SFC Boyd nailed it. Mentorship and your innate desire to be a leader. Being an NCO is is NOT about a raise in pay or the stripes on your collar and Leadership is more than giving orders. An NCO IS the example and as a consequence you always give 110%. You are proficient in all of the CTT and ARTEP tasks. You never settle for 61 points on individual events on a PT test and you are the first to complete the 2 mile run. But more importantly - you ALWAYS put your people FIRST. They eat first, they get the time off first, they bed down first and you ALWAYS ensure that they are safe. You are an NCO because of them. They look to you and you can never let them down (sorry for the speech - this sentiment was provided to me by CSM James B. Ellis upon my commissioning from OCS. It also holds true for the NCO Corps as well)