Back when I did random probing I'd probe blocks, something like:
1000:1000:1000
1800:1000:1000
2600:1000:1000
3400:1000:1000
4200:1000:1000
(so add 800 to the first number each time) Then when I'd done 5-8 of those I'd add 800 to the second number and start again, so
1000:1800:1000
1800:1800:1000
2600:1800:1000
3400:1800:1000
...
Once I'd done that block, then add another 800 to the middle number, I'd usually just go like that till I hit a planet, then change to somewhere else.