Triv, dont be scared to filter. Try it in small doses at first on sections of road you are familier with. You dont need to go bombing along either...infact, much the opposite. I filter relativly slowly, and every now and then check my mirrors. If someone if up behind me, I'll pull aside (when possible and safe to do so) and let them through.
Use common sense, and if you don't trust something and feel something bad is about to happen...slow down, or stop.
Be aware of cars with folded in mirrors (I sometimes ask if the driver would like me to fold them back out!), or no mirrors at all. Look for cars moving over in their lane, they might be about to change lanes or turn off...look for turning wheels aswell.
Also, check the car mirror - can you see the driver? If you cant, they cant see you. If the driver looks like they might be about to do something and you can see they havn't looked at you in your mirror, slow down (be prepared to stop) and toot your horn.
Rmember, the horn is to alert others to your presence; it is not a tool for "get outta my way fool"
thats what loud exhausts are for
(i joke, you should never actually try and force people out of your way, noisy intimidation or otherwise)