Everyone else has said these really, but this is what I do;
Get changed really quickly and get out of the door without thinking too much.
Set myself a route (always circular) and distance in advance - if I say to myself that I'll just see how I go, I always tend to do shorter distances.
If a long distance, choose a new route to try - therefore not thinking 'oh no, I remember this point and I've got miles to go'.
Spend lots of time breaking the run into, say, 8 chunks - visualise each part and then calculate where I am as a percentage, then a fraction
When it gets hard, make up a mantra, I suppose - 'I can do this, I can do this' saying a word each time my foot hits the ground.
Visualise something lovely I can eat guilt-free later.
Think who I can tell how far I've run and recording my workout on mapmyrun.
Plan my shopping list/to do list/holiday plans (whilst visualising myself in a bikini!)
If all else fails, buy some fab new kit!