Setting the proper tension on the blade seems to be the hardest part of sawing. The blade needs to be tight enough that it doesn't wander but not so tight that it breaks. Some brands of blades will take more tension than others. Here we will consider that you are using a top quality blade. On the Delta 16" and old C-Arm I set the tension when the tension lever lines up with the hump on the arm, from the left side of the saw this would be about 12:30, for a #5 blade. When I use smaller blades like the 2/0 the lever should start tension at about 10:30. And going up to a #12 the lever should start tension at about 1:30. So as you can see the tension varies with the blade size you are using.
The best way that I have found to tell when it's right is by actually sawing with the blade. Normally if you are breaking a blade before it is dull the tension is too tight. Too tight of tension usually breaks the blades in the center. You will know when the blades are dull. While cutting the feed pressure needs to be increased to cut at the same per inch rate, that is a sign of the blade getting dull. Next you may notice the blade is burning the wood instead of cutting it, then it breaks. That was a dull blade sign that you will learn real soon with practice. Back off a little on the tension and see if you don't extend blade life. If you back off too far you will start to notice that any grain to the wood the blade will deflect and follow grain lines, you just can't get the blade to run a true line in the wood. Tighten the tension a little and notice how the blade will start following the cutting line. When you find that point where it runs true the tension is right. Just check it and remember what it feels like when you tightened it and do it that all the time. With a little practice you will soon learn the feel for the proper tension. With the right amount of tension I get the same blade life out of a #5, at 1800 speed, cutting 3/4" pine as I do from a 2/0, at 1700 speed, cutting a 3 layer stack of 1/8" Baltic birch plywood. Those blades are pretty tough when they are set up right.
The smaller blades take a little less tension, and the larger blades can take a little more. Setting the right tension is really something that you need to experiment on, it just can't be shown or described. But I have tried to give you the basic theory here.