[numbskull]

As you release a cast, the acceleration on the spool is tremendous and dumps line much faster than the lure can travel through the air. You have to slow this spool speed so it matches the rate the lure is traveling or you get overrun. Casting brakes (centrifigual, magnetic, oil viscosity, or your thumb) produce smooth friction to do this. Ideally, as the spool slows, the braking action becomes less and the spool will continue to dump line at about the same speed the lure travels such that the force of the cast is not disappated pulling line off the spool. In a reel with centrifigual blocks, most of their effect occurs as the lure is released. How much you need depends on the smoothness and force of your casting stroke as well as the weight of your lure and the speed/action of your rod. You want to start with one or two blocks engaged, then add more if you experience overrun early in the cast.
Your reel will cast best with no spindle tension (just adjust it until you can barely detect any side to side play in the spool, then perhaps a fraction more), but this requires you to lightly thumb the spool to decrease spool speed as the lure slows from air resistance. How much depends on the wind and air resistance of your plug. With aerodynamic plugs, the bearing oil viscosity (experiment with the various Rocket Fuel products available) and casting blocks may slow things gently enough that you don't need to thumb at all until the lure lands. With bulky metal lips you need to let your thumb hover over the spool and apply light pressure to the line (or better yet the spool edge) as things start to fluff.
A little extra spindle tension can help reduce the need to thumb your spool, and if you are backlashing a lot later in your cast you should tighten it a bit, but watch out. On most reels friction builds VERY quickly as you tighten up, and it will kill your casting distance dramatically. It will also distort the spindle fractionaly and wear out your bearings much faster (or so they tell me). Basically, you want as little tension on the spindle as you can control.
Finally, the most important factor in avoiding backlashes with conventional tackle is the smoothness of your casting stroke and speed with which the rod unloads. Avoid trying to add acceleration at the very end of your cast (don't add a snap to the end of your stroke like you might with spinning tackle), and avoid fast action rods (at least when you are starting out).
Conventional tackle takes some getting used to, but it excels in many situations and you'll be a more effective fisherman if you learn how to use it. Good luck.