Do you have a boat?

What you are doing sounds fine. I don’t think you need a sinker in front of the jig – I’d just use the jig and minnow, unless you are talking about floating jigs, which can work well with a slip sinker and a short leader so the jig and bait run a foot or two off the bottom. Otherwise, the key to walleyes is finding the right spot at the right time. Fish weed edges and drop offs, experiment with different depths – you don’t need to fish real deep this time of year. Try fishing at night.

I like to sit above a hole in a canoe and jig with an orange or lime green lig head and a crapie minnow. I've also tryed with leeches, but the minnows work better

I like to fish rocky bottoms near steep banks in 10-15 feet of water. Play around with the depth until you get good strikes at a certain depth. Here's the method I've always had good luck with. I tie my own spinners with a hook, 4 small orange beads, and a brass spinner on a 36" leader (it'll be shorter once you tie the hook on and a loop in the top end). put a sliding sinker of some type above a swivel, then attach your leader to the swivel. Hook a live minnow, and troll slowly, keeping your sinker just off the bottom. Walleye will readily swallow a live minnow, even with a hook in it, so try to set your hook before they have a chance to swallow it. Sometimes, they'll just grab it by the tail, hold it for a few seconds, then take it into their mouth, hold for a few seconds, then gulp it down. I usually give them just a couple seconds of slack after that first tug, then set the hook and drag them in. I've been using this method for MN walleyes since I was about 4 years old.

As your lake gets warmer throughout the summer, they'll tend to move deeper, but also try to find some lake-bottom springs, which can make for mid-summer walleye hot spots. Snorkeling is an easy way to find springs. Just dive to the bottom, and swim around. When you feel a cold shock, you've found a spring.