One of my biggest frustrations with setting is when I see climbers struggling to read the sequence I intended. Not frustration with the climbers, mind you, frustration with myself. For me, I feel like I've failed in my job when this happens, even if the climbers themselves don't get too upset by it.
I've learned that the way to avoid this problem is to ensure that you are directing the climber into your sequences through the holds you choose, and the way in which they are positioned. Donald Norman, a innovator in the field of design, describes how you can use 'signifiers' to direct a user to discover the 'affordances' of an object. Remember, an affordance in a route-setting context is simply the ways in which a climber is able to use a hold.
When setting, there's a number of different signifiers we can utilise, and many which we can simply take advantage of. The most obvious signifiers are built into the shape of holds. Consider these two examples of holds.
The first is a set of 'Basic Edges' from Metolius. No tricks here. The no-frills design and pronounced edge communicate clearly to the climber that the most effective use of this hold is to grasp the positive edge. Obviously, you could flip this hold and use it as a foothold in your setting, but it's not ideal. Why? Because the design of the hold communicates to the climber that it's a hand hold, and will probably lead to climbers attempting to undercling the hold and coming out of sequence.
The second is a creepily awesome looking volume called 'Neuroid' from SoILL. Through it's design, this hold doesn't communicate much at all. There's a whole host of ways to grasp this hold, and without feeling each edge and angle, it's unlikely that the shape of the hold itself would lead you to intuitively grasp the most positive edge. Unchalked, it gives away nothing about it's affordances.
Chalk is another obvious signifier, albeit often an unintended one. As a climber, if you're gearing up for a deadpoint to a hold you're unfamiliar with, you're going to aim for the most chalked up portion of the hold. Why? Because the presence of chalk is communicating that most people held the hold here, and it's likely to be the most positive edge. Although chalk is often an organically occurring signifier, it is possible to utilise it from a setting point of view. In many competition sets you'll see tick marks and pre-chalked up holds. This is an obvious attempt to direct climbers, and an effective one.
Another helpful strategy is to attach jibs to arêtes or the corners of volumes as very subtle thumbcatches. While they give almost no extra purchase to the hold, they communicate to the climber that the feature is intended to be used, and increases the chances that they'll identify the intended sequence.
There are many ways you can utilise signifiers to direct your climbers, but there is something else you need to consider. Should you always try to direct climbers? You might say,
"Why make it so easy for the climber? Route finding is part of real rock climbing, so what's so bad about confusing routes inside?"
This sort of question threatens to open a whole, debate-filled, can of worms, and I don't want to adjudicate one way or another, other than to make a simple point. It's not that you should always direct a climber into your sequence in the easiest way possible, or that you should not. Rather, you should always be aware of what you are communicating to the climber through your choice of holds and other signifiers. Sometimes it makes sense to set a climb for which confusion or 'sequency-ness' is part of the character of the route (Like this). Although more often confusion is not intended - it's simply poorly thought out route-setting. As ever, work out what you're trying to achieve, and then ask yourself if the route you've set does that thing.