There are thick spoons. There are thin spoons. Never the twain shall meet, at least in trout fishing. Thick spoons run deep and as such are best for reaching down to early-season trout in fast water. Use the smallest available sizes on small to midsize streams.
Basic colors are silver or gold, often with colored stripes or spots added.
Cast up and across in deep, fast water, but don't use a steady retrieve. The art of trout fishing with spoons is in reeling just fast enough to keep a tight line while pumping the rod tip to give a darting, tumbling action to the lure. A steady retrieve will catch some fish, but an erratic retrieve will catch more. They work better later in the spring when the water is shallower, a little warmer, and trout are more aggressive. First, use these lures in sizes suited to the water you're fishing.