You didn't say how deep you are fishing. If you are in shallow water, you might want to downsize that leadhead. Unless I am working with high water conditions, or fishing deep in fast current(deeper than 25 feet) I hardly ever fish 3/8 in summer. You want to use the lightest weight you can get away with in the current at the depth you are fishing. On the Upper Delaware river We rarely go over 1/4 oz in summer, usually more like 1/8 or maybe 3/16. The average depth is about 4 feet and the current averages 2-3 MPH. The fish tend to be shallow this time of year, so we don't spend much time in the really deep holes, but even when we do fish deep, I usually use 3/16 or 1/4. A fast or extra fast medium or medium light action 6 1/2'-7' spinning rod with 6-12 lb Fireline or braid is a must. We used mono for many years, and caught a lot of fish on it, but the sensitivity is so much better with braids that once you try them, you will never go back to mono. Being thinner than mono or flourocarbon, Braids cut through the current better too. Flourocarbon has good sensitivity, but can't stand up to the abuse of a rocky river.
If you are fishing from a boat, Cast at roughly 90 degrees to the bank. Casting a little more upstream than 90 degrees will give the jig time to drop, but if the water is shallow, it may hit bottom before you can take in the slack. Once you get that slack in, you will probably be hung up. Even if it is deep, casting at too big of an upstream angle, you jig will hit bottom and snag before you feel it hit. At that point, you are likely snagged. If you are going downstream and cast ahead of the boat, you won't feel bottom until you are already past your jig, which will already be hung up. If the boat is anchored, or you are fishing from the bank, wet wading, etc. you will have a little more latitude. Cast a little upstream to get the drop going. Pick up your slack quickly, and start your retrieve when your jig is starting to tick bottom. Swim the jig slowly, and lightly pop it off the rocks it hits as you drag it along. Too much lifting and jigging your rod will just keep the jig from dropping. Smallmouth and walleye will take a bait being pulled slowly across current, upstream or hanging in the current. Walleye will rarely take a bait retrieved downstream. Smallmouth and trout being more active swimmers are much more likely to take a bait retrieved downstream than a walleye, but with jigs, your best bet is swimming across the current, then a slow upstream drag. Bass and walleye will even hit a jig on a dead stick in the current. If they don't want slow, sometimes you can trigger a reaction strike by letting the jig drop, swinging it across the current, then ripping it in before it is hanging downstream.