Grasshoppers are great to fish on a stream or a lake. They are a large fly and therefore readily visible to the fisherman. Hoppers can serve as strike indicators therefore, sometimes it is worth using a large pattern with a parachute for high visibility. So if you are fishing nymphs it is worth considering a hopper as an indicator. In addition, if you consider the size of the grasshopper next to say midges, caddis or baetis, it is a great meal for a trout and will certainly tempt them in the correct circumstances.
Therefore always carry a hopper pattern or two in your fly box in summer when the hoppers are likely to be out.
Think where the hoppers will hit the water. On a windy day they are apt to be blown a distance when they are disturbed. As a young boy, I fished lakes with a lot of grass on the edge. In the height of summer one would walk through the grass and hoppers by the dozens would jump ahead after disturbance. The technique then was to walk towards the waters edge through the grass. Inevitably the hoppers would fly ahead, and particularly if their was a breeze behind they would fall onto the water where the trout would feed on them ravenously.
Hoppers will generally be fished dry. When casting a hopper, don't be fussed if the fly hits the water noisily. Essentially that is how the hopper will land on the water if it misjudges its landing or is blown there. However a fish can sometimes be spooked in bright light and shallow water if the fly lands too hard. Where circumstances permit I will cast the fly so that it hits the bank of a pond or stream and let the fly fall into the water under its own weight. That enables the fly to fall on the edge of the water close to undercut banks from whence the larger trout cometh.
When a hopper is on the water, it may struggle intermittently. It will sit low in the water, so in gentler rivers or ponds, a smaller pattern which will sit lower in the water tends to have more success. On the other hand, in broken water, a more buoyant pattern will float longer and will be more visible.
There are a range of hopper patterns available. As trout are opportunistic feeders when it comes to grasshoppers, there is no need to try and match a particular type of hopper. However, it is worth taking note of the hoppers in the area to get an indication of size. Generally I will fish a smaller hopper, say a #10 to #14 however if you a floating in rougher water, the larger hopper will stay afloat longer and will be more visible. A parachute hopper will also be more visible in rougher water.
In the shop we carry a large range of hoppers from #6 - #14.