To install the mod properly you need to get the JSGME Tool first and install it in the right folder. You will find the tool under: www.rofmods.com
Select JSGME Mod Manager and then click on download like in the pictures.
Navigate to your download folder and extract the compressed file via Winrar or something similar to your main Rise of Flight folder:
In your Rise of Flight folder you should now find the following marked folder and data:
Now get back to www.rofmods.com to download the advancing soldiers mod:
Select Advancing Soldiers and press the download button:
After that navigate to your download folder once more and extract the file into Your Rise of Flight folder/mods
Now run the JGSME Mod Manager to activate the mod:
If you installed everything in the right place the mod should now show up on the left side of the mod manager under available mods. Click on it and move it to the right side under activated mods. Then close the mod manager and start Rise of Flight. You don't need to deactivate the mod again when you want to fly on a server that doesn't use it.