Gurfateh!
I prefer the self mind trick method- recommended by Giani Thakur Singh Ji DDT. If doing mool mantar (out loud) then recite wahgeuru after each aakhar e.g. Ek Ounkaar Waheguru Satnaam Waheguru Karta Purakh Waheguru. etc. This keeps you focusing as you are trying to concentrate and get it right. After 40-50 recitations you might find you have the hang of it, then stop saying Waheguru out loud (here say it in the mind) and continue it mool mantar out loud. It should start jaap of Waheguru inside you.
Also when trying to concentrate on Bani use the same method at the end of each bhangti say waheguru and do the same for the rest of the Bani. This should help with concentration and is a beautiful way to recite Bani.
This information was taken from Gianijis katha on Sukhmani Sahib paath.
Best of Luck
Gurfateh!