Transposition is a topic that is a concern for most horn players in high school and beyond. To help horn players get a basic grasp of the easy transpositions, and maybe a better grasp of some of the more uncommon and unusual transpositions, I made this document:
French Horn Transposition Explained:
You can also get .PDF copy of this file by using this link.
After you have a good grasp of the mechanism of transposition, make sure that you take the time and include it in your regular practice (especially if you don’t play orchestral repertoire in other keys regularly). Some of the best practice for just picking out simple songs (preferably in the key of C) and practicing them in different transpositions. Once you get comfortable, the Kopprasch studies (also available on Amazon or WoodwindBrasswind.com) (especially the early ones) make excellent transposition practice pieces.
Once you have a good grasp of the skills involved in transposition, you’ll find that it is easy to flip the “transposition switch” in your brain and read in E, or D, or G, or any other number of keys as naturally as you read horn in F. However, just like learning a language, 5 minutes of daily practice will do more good than 2 hours once per week.