When I read this quote by Sister YasminMogahed, it made me view the dhikr of 'La illaha il Allah' in a totally new light:
'The process of first emptying the heart can be found in the beginning half of the shahada (declaration of faith).' Yasmin Mogahed
When you do this dhikr, imagine that every time you say 'La illaha' your heart is emptying out all that is distracting it from Allah, like a cup spilling out its contents.