If you are into sports, specifically tennis, you can always become a fan, or you can be a player, or you can be a tennis coach. If you believe you have what it takes to become one, you should no hesitate becoming one.
You may start and target lower level leagues, or if you are more confident about your skills or if you have prior experience, you can target high school or college players to coach. The professional league may follow only after you have proved what you can do in these leagues.
If you have been employed, you need to know how you can effectively lead your players to victory. First, you should organize your thoughts. Make sure you have plans on what you want to happen, in general and in specific terms. You also need to determine what you want to achieve on certain time frames.
It is important that you make your player understand what you want and what you want him to do. You should be able to convince your player to stick to the game plan. This will be your test of trust and, maybe, loyalty.
You need to keep in mind that in high school, or even college, there can be kids who still do not know a lot about the basics, hoe much more for the advanced skills. You should never expect that they will know all, even just the basics. This can never be right. What you need to do is to start from the very beginning, even if some already knows what you are going to teach them. This can be a way for you to assess the capabilities of each of your players.
As a tennis coach, you also need to consider what your players want to achieve. You can work together to the fulfillment of those goals. You can teach a basic step, refine it and let your player master it. The same method will be followed when you are teaching the more advanced steps. But, in both of these levels, you need to consider the skills of each of your players.
You can use whatever strategy you like. But it is recommended that you stick to the traditional way of doing things. This can be explained as starting with the most basic steps. After proper assessment, you will be able to determine whether your player is ready to move on to a higher level.
Continue to do this until your player has mastered a skill level.
If you want, you can seek help from professionals and ask for advice. There are also books on how you can recreate yourself and grow as a tennis coach. Lastly, what you can do is base what you teach your player and what you believe is right.