First make sure you don't have a cracked or leaky exhaust manifold. That will make a light ticking noise. You can do this by a variety of methods including just running your hand around the manifold (be careful not to burn yourself) feeling for the leak while the engine is running. Check the seal between the manifold and exhaust pipe. Especially check the heat riser valve.
If not an exhaust problem, pull the valve covers off--or just the one on the side you hear the noise.
Visually inspect the rocker assembly for anything odd. Sometimes, you may have a rebuilt engine with the original rocker arms. You may have one that is worn out. With the engine off, grab each one, revolve the engine and feel them. They should all have the same type of movement.
Finally, consult your G.M. or V8 engine manual for the procedure of adjusting the valves. It is not difficult, just time consuming. I always run them down to zero lash and then go 3/4s more. I think the G.M. manual suggests one full turn after no lash. Some people run less and more. Whatever works for you.
If you still have the noise after checking the exhaust, verifying there is no obvious wear on the rockers, and setting the valve adjustment--then there is very little additional you can do without tearing the whole motor down.
However---noises can be very tricky. Drop the V-belt assembly off the car and crank it up. You may find the noise is gone. If this is the case, you have an alternator or air pump that is failing.