Depending on where you are and what you're targeting, fly fishing can range from relaxing to downright frantic. Anyone who's ever sight-fished on the flats or chased busting fish around knows that speed and being ready at a moment's notice can be of paramount importance. When fish show up in a flash, your casting window may only be mere seconds—and you need to capitalize on that if you want to catch fish!
1.) Watch your feet- This is kind of an obvious tip, but it's a mistake people (including me!) do make. Your feet may be clear of loose fly line at last glance, but due to wind, re-positioning your feet, or other factors, the line could now be stepped on or wrapped around an ankle without you knowing it. This is especially true if wearing shoes since the sense of feel around your feet will be substantially dulled. If possible, not wearing shoes is an easy solution to help increase your vigilance regarding the line's whereabouts, but it's also often necessary to constantly look down to make sure the line isn't being (or in danger of being) squished or tangled around you. Speaking of which, a common time for this to happen is when quickly setting up to fire out a cast. Some folks have a tendency to nervously re-position their feet as they cast which can result in loose line being trapped and thus a possible blown presentation.
2.) Keep slack line clear- This is closely related to the first tip, but when fishing from a boat or shoreline, making sure any slack line on the ground is clear of stuff is important. It's amazing how fly line can seemingly find just about everything to tangle around. A lone stick on the ground, a cooler handle—if it's there and you're not vigilant enough, there's a great chance the line will eventually encounter it. Keep an eye on your slack and manage it as best you can before each cast.
If I'm stationary and waiting for the fish to come to me, I'll typically lay my slack line out in an orderly, unobstructed fashion so that I can make a fast presentation without any worries of tangles. A trick I like to utilize when standing-in-wait on the front deck of a boat in breezy conditions is to lay out my slack line behind me in the main cockpit of the boat rather than on the front deck itself. With the line sitting down lower in this deeper portion of the boat, the wind will have less of a tendency to blow it off the deck or around something like a cleat. A stripping basket or bucket can also be useful tools for managing excess line.
If I'm walking a bank or beach without a stripping basket, I'll typically hold some spare line neatly but loosely coiled-up in my non-casting hand if the terrain is craggy or snaggy. If I'm walking a shoreline that won't snag or damage my loose line, I'll often just drag it to the side and behind me as I walk. That way, if I spot a fish, the line should be clear of me so I can simply stop and cast instantly.
3.) Have the fly at the ready position- Whether walking or aboard a skiff, I often like to hold the fly as I'm moving. In some instances it can simply be dragged alongside you in the water by the rod, but there's more of a chance of the fly getting fouled by debris or the hook becoming dulled from contacting something hard when doing this. Holding the fly avoids these issues and when a fish is spotted the fly can just be flick out in the water and the first cast begun. I find the safest way to hold a fly is either by pinching the hook bend behind the point, or better yet, staying clear of the hook altogether by holding onto the fly's tail or any long fibers behind the hook.
4.) Have enough line out- In order to make a fast cast, just managing your loose fly line isn't enough—you need to have enough fly line outside of the guides to actually initiate the cast quickly. If you're standing there with some of the leader butt in the guides or just a couple inches of fly line outside of the tip-top, there won't be any or enough of the fly Iine's weight outside of the guides to get any solid casting momentum started. I like to have at least a few feet of fly line outside of the tip-top guide as it's easy to manage yet still affords me just enough of the fly line's weight to get the cast started rapidly.
Be ready and catch more fish on the fly!