If you absolutely must cross open ground to get to a marine, vary your path as much as possible.
Actually, before you do that, ask yourself "do I HAVE to run out in the open?" Too often I see people charging marines for no good reason whatsoever. If they're in an open room with nothing in it, why charge them? They're not presenting a threat there. Get inbetween them and the nearest important objective (hive, RT, empty res node, siege spot, whatever) and get into a good ambush spot. If at all possible, let them come to you. And a marine building a res node is not an immediate threat. Which is better, to let him build the node, then kill him when he rounds the corner, then go eat down the node before it even earns back its cost, or to rush at him, die, and let the node stay up unattacked for a few minutes?
Anyway, back to that open ground. Use any and all available cover, even the tiniest bit of pipe or whatever, to get as close as possible. Then if you have to charge, charge, but do it in a randomly zig-zagging pattern. Don't strafe in one direction too long. If you can bhop, do that, but don't even do that too long because it's predictable.
When you do manage to close that gap, stick to the floor. It's your best friend when actually attacking. The instinct (and I'm guilty of this too much myself) is to bounce around madly while biting. There are a few problems with this. One, it brings you right up in front of the marine's gun, taking away your vertical advantage. It's harder to aim down and track a target, so try and make him do that. Two, it can throw off your own aim when you bounce like crazy. And three, it's harder to adjust your attack angle. On the floor you remain in control, you can change direction instantly. If you're in midair and that marine jumps away from you, there's nothing you can do until you hit the ground again. You can't twist and immediately follow him in the air, you just have to finish your jump arc. This is often where skulks get killed, is in midair while bouncy-attacking.