You can use After in [Unit] section to define a service that should be started before your service starts. For example if you are using NetworkManager, you can make your service start after NetworkManager is started. Also you can bind to it (use BindsTo) if your service is network dependent and also fails if network does:

[Unit]
Description=test service
BindsTo=NetworkManager.service
After=NetworkManager.service

You can use After in [Unit] section to define a service that should be started before your service starts. For example if you are using NetworkManager, you can make your service start after NetworkManager is started.

[Unit]
Description=test service
After=NetworkManager.service