1.  Depthfinder.  With it, you're fishin.  Without, you're just wishin.

2.  Troll until you hook up with walleye

3.  Slow down and jig or cast cranks until the bite stops.

4.  Lather, rinse, repeat.

Pretty much everything else you need to know...lures, depths...has already been covered. 

The only other thing I will say is when you hook up while trolling, pay attention to the conditions around you and then try to duplicate as many of them as possible as you search for your next spot.  You'll quickly find out which of the variables matter on this particular day and which don't.

A partial list of what to watch for (in approximate order of importance):
Depth
Bottom content
Location (reef, point, saddle, flat, open water, weeds, etc)
Wind direction
Sun direction/penetration
Lure speed
Lure action
Lure color

After awhile you can go from lucky, chance encounters to targeted fishing with a high probablility of success if the fish are active...and you'll be on the most active fish in the lake more than likely.