Developing a paintball course can be a difficult and long process. There are many things that must be considered before diving into the field. You obviously know enough about the game of paintball and what makes a good course and what doesn't or you would not be reading this now. How to make a paintball course involves some of the most obvious considerations: location, type of game (woods or speedball), size of the field, cover and concealment, originality, staging area, rental/purchasing area, and concessions.
Location, when discussing a paintball course, can mean several things. First, is the location of the course easy for potential players to access? Is the location easy to see from a heavily travelled area (does it advertise itself)? Does the location offer the size and potential for what you want to create (you need to consider parking, sales, staging areas, and SAFETY)?
The type of games that you want to play at your course is a big one as well. If you want to play woods ball, then you obviously need a good sized hunk of woods (a few acres minimum). For speed ball the possibilities are endless (an open field with different types of cover and concealment scattered throughout). Either course holds a pretty common requirement of having some sort of centralized "fort" at each end of the field. There obviously needs to be a goal during gameplay and frankly, just trying to shoot everyone on the other team gets a little old. Thus, the "fort" at the other end of the field holding a flag or something of value that needs to be guarded by the defenders and captured by the offenders provides for an upbeat variation in the game.
The more elaborate your course, the more interest it will hold. Players will play paintball anywhere. They play because they like the game, the adrenaline, the excitement, the thrill. However, if you, as a business owner or paintball field manager, have competition from nearby paintball courses, you must have something that "wows" your customers. The players need to have a reason to want to play on your field. Do you have a castle? Do you have some buildings? Do you have awesome cover and concealment throughout? What's different about the course that you're going to build? What makes you stand out?
The size of the field, mentioned a few times above, is basically dependent on the type of game you want to play. You can get by with a very small field. For speedball, it's sometimes better to have a smaller field. Games will go faster, it's easier to see, and players will keep moving. The size of a football field can be about right for 5-10 players per team.
For woods, it's difficult to say what's a good size and it really depends more on how many people are going to be playing. A football field seems bigger when you're in a forest. Either way it is a lot of ground to cover. However, many times with woods games teams can be much larger. Large scale attack and defend or capture the flag games are fairly common. As the business owner, you have to think that more players = more profit. You want to have the capability of serving as many players as possible. Building 2 fields next to each other with white engineer tape down the middle splitting it (the long way) might be good way to provide more room for larger games, yet you could use just half of it for smaller games.
Cover and concealment is an absolute must. Players need to have something to hide behind and utilize as they move forward assaulting the enemy. There also needs to be a decent balance, not too much cover, but not too little. You won't really know until you play on it.
For speedball, cover and concealment may be less important, since you're trying to have the games get done fast (hence speedball). You may want to consider placing items on the course that can be easily removed throughout the day.
Rental/purchase area and concessions are some topics that will need the research. For this and all that's mentioned above, your best source of info is other courses. You can view pictures online, but playing at other courses would give you the insight that you need. Take a notebook along and write down things that are good and bad about it. What would you like to see, what can be improved? The same type of review should be done during the development of your course. Have your friends come by and play or offer a free day for players to come and try it out and provide feedback.
Don't forget to enjoy it. If it's stressing you out, then you're not doing it right. Do your research, accept feedback, and make changes. Good luck!