When a child is learning to write in a classroom, they may be instructed that there is one specific way to make the letters, that the strokes need to be made in a specific order and in a specific direction. If your child is learning to write at home, if they learn to make the letters in the way they will be taught in school, it may save them the frustration of having to un-learn and re-learn a new technique later on.
For example, for an upper case “M” they may be instructed that they begin at the upper left and make a vertical line down. Then, depending on the handwriting style taught at their school, they may be instructed to put their pencil at the upper right and make another line straight down, then put the pencil back at the upper left to make the first diagonal down and then back to the upper right to make the second diagonal down stroke. If a child is already making what looks like the exact same letter, but is making it by starting at the lower right and going up, down, up,down without ever picking up his or her pencil, he or she may be told that it is not correct, even though the end result looks the same.
A kindergarten classroom I volunteered in had a very old set of plastic letters with bumps molded into the plastic. By running their finger over the letter, children could learn what direction (i.e. top to bottom, bottom to top, right to left, left to right) they should move their pencil when writing letters. Although this cardboard set won’t last nearly as long as the plastic ones, it will cost you practically nothing to make.
The set shown here is just made from tag board, with letters drawn free hand and then notches cut with an Exacto knife (obviously an adults only job!). The notches are pushed loose from the board so that the letters will feel smooth if the child moves their finger over it in the direction their pencil stroke should go, but will feel rough if they run their finger over it in the opposite direction.
You probably shouldn’t assume that you know for sure the direction preferred by educators when making the strokes for the letters. I’d recommend using a website such as http://www.first-school.ws/theme/handwriting.htm for reference. If your child is already in school, or if you know what school your child will be attending, you may be able to check to find out which of the handwriting styles they teach so you can make your letter set match that style.