There are several very useful PC and web based tools to allow you to create routes from the comfort of your own home and also various phone apps which allow you to follow or check your course whilst out and about.
On the PC, tools such as GMap pedometer allow you to create new routes via an online map tool where you can click simply through your route and then save as a GPX file to then view or transfer to your phone. Other tools include Strava and Garmin Connect which do a similar thing.
Once you have a GPX file you can format this in a way that downloads to your GPS watch (I may write a blog on this sometime) but you can also download it to your Android or iPhone and use freely available applications to follow your route on your phone.
Most modern Android or iPhones have GPS enabled on them which makes them a very useful tool for viewing your route whilst out running. They are not the best tool if you are racing, but as a check on your route when exploring a new area or checking out a new route or race, it is an excellent check on where you are going.
As an Android phone user, my favorite apps are OSMAND and GPX Viewer. For both apps you will need to download a GPX file to the phone and the easiest way is via email. Save the file to the normal downloads folder. GPX viewer loads up the standard Google map and provides a menu "Load tracks" which allows you to load the GPX file directly from the Downloads folder. Upon load, the map zooms to include the whole route. If GPS is switched on, you can then see your own position in relation to the Google map and with the GPX route overlaid in Blue. The only difficulty with this use of Google maps is that it requires that you have a data connection which is not always available way off the beaten track.
OsmAnd on the other hand is an offline mapping tool that can provide sat nav functionality as well as route finding via waypoints. This is great as it works even when you have no data connection or mobile phone connection. As it runs offline, you have to download a file for the area you are in (for me, this is England only, although you can download accurate maps for most of the world even including places like Scotland). Once you have downloaded the online map (Via settings - manage map file) you can then use the "map layers" menu to load a GPX track. Unfortunately this app only looks in one directory to find your GPX files. You will need to copy your GPX file using an app such as "ES File Explorer" to a directory called tracks in the directory /sdcard/osmand. If the tracks directory is not there, you must create it first.
The result of using these tools is the ability to follow your route on your mobile phone and if you make a mistake, make adjustments quickly so that you do not go too far off course.
The images are taken from the OsmAnd and GPX viewer apps for part of the Green man ultra route around the Clifton Suspension Bridge.