1. The Prophet (SAWA) and his holy Progeny (AS) guided us to pray our prayers thinking as if it is our last prayer before we leave this world. إذا صَلَّيتَ فصَلِّ صلاةَ مُوَدِّع
This way of thinking makes our heart and intention in the Salah and not away from it.
2. 'It is also very useful to remember the fact of our leaving this life sooner or later as death is ordained in all of us. A time will definitely come when we will be in our graves. This will make us focus more in our prayers.
3. 'We also need while praying to remember our sins and our need for forgiveness. This will make us more humble and more dedicated in our prayers.
4. Remembering Paradise which is the place of sincere servants of Allah, and hellfire which is the place of disobedient, helps making us more dedicated in our prayers.
'There are many other ways to increase our concentration in Salah.
Wassalam.