If you can write well rounded, simple yet effective programs, you will be far ahead of most in the industry. Your length of engagement will be huge as you can help people get the results that they want/need that much faster. How do you get better? Here are a couple points that helped me get started.
1..Write a lot of Programs
I wrote 101 programs last month. Some will call it crazy but...i love it. I love tinkering with programs after they are ran and figuring out different ways to implement different specializations. Much like anything in life, the more time you spend practicing it, the better you are going to be. The first program that I ever wrote is still on my computer and I use it as a example to my staff on not what to do...it was terrible.
How do you put this into practice?
For new coaches, grab anyone that is willing to workout and write them a program. Does you 60 year old mother want to workout? Write her a program. Does your brother want to get a bigger squat? Write something specialized for that.
They should run the program in its entirety and as it is written (that does not happen sometimes). When they return to you, make sure you get feedback and learn how you can make the programs run even better.
2..Different Is The Same...Most of the Time
If I were to poll 3 strength coaches and asked them to write me a program with the exact same parameters, 90 percent would be the same across the board. Some may prefer to back squat, others may utilize a trap bar...some like using Olympic variants and others may not even include them. Does this mean that one is better than the other? Nope...
Same thing with speed/agility exercises. We have a bank of exercises that we use that have shown us great results time and time again. Are there other exercises that can be used to accomplish something similar? Yes.
No matter what tools (exercises) you use, as long as the same principals are the same, outcomes should be similar. I personally love this as it gives you the artistic freedom to craft unique programs based on individual need.
However, if you have a 70 year old client with banged up shoulders, I would not recommend heavy power cleans...this is an extreme example but...you need a good knowledge foundation before you can start getting really creative with your programs.