These guides will go through a number of methods to use when drawing in perspective. I myself use these when I draw in three point perspective but they should work just as well in two point perspective, one point perspective or parallel projection.
A few things to know for these examples to make sense to you are a few basic things about perspective drawing. The guides will mostly be drawn entirely flat so they are easy to comprehend, there will be perfectly horizontal and/or vertical lines drawn without them starting or ending at a corner or intersection, these lines should be drawn from the vanishing points in your drawing.
What is a vanishing point? If you have bunch of parallel lines in a perspective view they will all end up at the same single point if let them continue towards the horizon, that point is thus a vanishing point. All new lines drawn from that vanishing point will be parallel to the lines you used to find it.
To get exact proportions and avoiding rounding errors all these methods are based on zero calculations and zero measurements. Instead these methods are based on reference lines drawn between different points, being vanishing points, line ends and line intersections. The key element here are intersections, by having lines cross each other we make new reference points to use for even more lines, this way everything we do is in relation to what you started out with.