You need a balancer. The best one is the Koll Rotor Pro, and you can get it from heliproz, etc. There are less expensive balancers out there too, but the Koll is worth every penney IMHO.

To match cg, what you do is find the point near the center of the blade (lengthwise) where it balances perfectly. You could use the edge of a ruler clamped in a vise as the balancer, and just move the blade from side to side until you find the balance point. Mark it. Mark the same point on the other blade, then put it on the ruler and see if it balances at the point where you marked it. If not (which is very likely), you will need to add some tape to either the end or the root until it balances at the mark. Now both blades will have the same lengthwise cg. Next, you have to made sure both blades weigh the same. You can use a very accurate scale if you have one, or you can put the blades on a see saw. You could make a see saw with a piece of scrap plywood by drilling holes at each end and bolting the blades to it. Mark the exact center and slap it back on your ruler--instant see saw balancer! Add tape to the light blade right on the cg mark you made before until the blades balance.

With the Koll, all of this is very easy and accurate. I use Monocote sticky back trim cut into strips for balancing tape. Works great and lasts longer than electrical tape, but electrical tape will also work.