Caution: broken glass

When you've dealt with the first few enemies on the first bridge, get on the lower deck and move along. After clubbing the snoozing Grunts, you can have fun with the Jackals pacing up above. Wait until one is walking over a glass panel, then shatter it with a shot from your weapon of choice, causing him to drop down to your level. Continue the fun by moving in and tagging him with a plasma grenade while he's still recovering from the fall.

You can also do the broken glass trick from the top deck of course. It's fun to do this with the gold Elite later. Tempt him towards you and shoot the glass from under his feet just as he thinks he's got you. You can drop down after him if you want to be aggressive; or just lob a plasma grenade down there and see if he leaps off the bridge.