This tutorial will hopefully cover how to make your game's Plot. This tutorial is also a good start, if you want to know how to get started on making your game.
Do whatever you need to get inspired. This can be done by playing other RPGs (This sounds rather silly and somewhat copy-cat like. However, if you only base the plot on what you play, or whatnot, it shouldn't be considered copying off of someone. At least, not if you make it original, and in your style.).
Some people may find inspiration from films, television shows, or anything that involves stories. In order to keep these ideas true and consistent, do whatever you need to keep the ideas the way you like them, such as wording it in your favorite word processing software, or working on your game and occasionally looking at the whole game, from start to the current state of development (Or end of the game, if you already have finished it.).
Play the game yourself. Without testing it and trying to see if there are any problems, you risk very highly of causing many players to be confused and frustrated. If a certain part of your game is frustrating to you, as you created the game, imagine someone who doesn't know what to expect, reaching that part? They may give up, without trying to understand why it is so difficult.
Get input from others. Only because a certain element in the game makes sense to you, it doesn't necessarily mean it will to others. For example, a certain area may look like there's been a conflict from long ago, and if the backstory behind it is that there was a big storm that caused it, it may not make sense, especially if the area in question is far away from a body of water.
However, the input from other people should give you a rough idea on what will make sense. Remember, if they are telling you that something seems odd or that it doesn't seem to fit, don't be offended. Just try to take it lightly, and try to improve the game. That is why this step is essential.
Try to customise it! The title screen should be custom made, essentially like a book cover. If you wish to attract players, you need to provide an image that will captivate attention. Remember, if your game's title screen captivates the attention of others, know that you may have more gamers. In a sense, the players who love your game are unknowingly advertising your game, especially if they recommend it to their friends, and so on.
Essentially, a good game is one that takes a long time to make. This means putting some time aside for this, and making sure it is rather decent and somewhat comprehensible. If something is impossible to achieve in the game, such as needing to collect 100 Gold pieces to advance, and the player can only obtain any number shorter than the goal, and it is clear there's no more ways of achieving the goal, it is not fair to the player. Doing things like that will result in many discouraged players, so, if there's a goal, try to make it at least achievable, occasionally getting some characters to hint on what to do next.