1. Choose the right skewers
You have two choices and both have their strengths and weaknesses. Metal skewers can withstand the heat of the grill and can be washed and reused, but they get very hot. If you're planning to serve kebabs to guests directly from the grill, wood skewers are a good alternative. Wood skewers won't burn your fingers, but they must be thrown away after one use and they char easily. Many cookbooks recommend soaking wood skewers in advance to keep them from scorching, but I've found that doesn't work very well: The heat of the grill usually dries out the wood quickly and the skewers burn anyway.
2. Use two skewers per kebab
Threading ingredients on two parallel skewers can be tricky to master, but this method ensures that the pieces lie flat and don't spin when you turn the kebabs.
3. Cut ingredients into equal-size pieces
On the same skewer, put similar-size pieces of vegetables, meat and fish that cook at the same rate. Nothing's worse than a kebab with dried-out shrimp and undercooked onions. If you're using shellfish, like shrimp and scallops, cut the other ingredients to match their size, and be sure to skewer them with only quick-cooking vegetables.
4. Space out the ingredients on the skewer
It's best to thread the pieces so they're barely touching or have a little bit of space in between them. This allows the heat to circulate around the food so that everything cooks completely and evenly.
5. Add unexpected ingredients for extra flavor
I've found that interspersing fresh, aromatic leaves on my skewers really livens up a kebab. I've tried sage, kaffir lime, basil and bay leavesall are fantastic. For maximum flavor, I thread them so the leaves are next to a protein. Also consider pickled vegetables: peperoncini, pickled cauliflower and okra are all hardy enough to stand up to skewering and taste delicious when grilled.