The best way to learn to lead any step is to look at it from the standpoint of the follower. Once you know what the follower does, you will have a better understanding of what you need to do in order to lead it.
The same is true of distinguishing between the lead for two similar steps: Analyze the difference in the follower's movement between the two patterns, and you will better understand how to clarify your intention of one over the other.
So ask yourself this: What does the lady do differently on each of the patterns? Well, we know that they both begin with a natural heel turn, so steps 1 and 2 are more or less the same. The difference starts to show around 3-4. On the Twist, the lady runs forward forward around a small circle, while on the Telemark, she rotates more abruptly into a side step, and then further into a back step with right side leading. From this perspective, you as the leader can see what you need to do in order to produce this action in the lady.
Omitting the heel turn altogether, what do you think you'd need to do in order to lead the lady to walk forward around you? Think about what you do on a standing spin: You place yourself on the absolute center of a small circle and carry your right side back, causing the lady to walk forward towards your right side. As long as your right side continues to move backwards, she should continue walking forward along the perimiter of the circle. The key is that you must cause her to move forward, and not overrotate her to take a side step (or worse, a back step) on her LF.
From your perspective this is a "Spot" rotation, which means that your body should not travel progressively through space, but that at least one part of your body needs to remain as a fixed point in space. Depending on who you talk to, you will either have your weight split evenly between the feet, having a fixed axis running down your centerline, or you will favor weight towards your left foot, with the axis running through your left shoulder, hip, and foot. Either way, your right side moves back around your left side, drawing the lady forward progressively. Bottom line: Man's rotation is spot, lady's rotation is progressive.
Now let's look at the T-mark, again minus the heel turn. The first notable difference is that the rotation is progressive for both man and lady. You both move sideways as you rotate, however, since the lady is on the outside of the rotation, her side step is slightly larger than yours. Whereas on the Twist Turn, you were the centeepoint of a circle and she ran forward around the circumference, here on the T-mark you are both dancing *sideways* on cocentric circles, where she is on the larger, outer circle.
Progressive rotation means that both side of your body move in the same direction, although one side is moving faster than the other. So if the direction of the progression is DC, that means that both your left and your right side must travel towards DC, even if your left side swings forward and ultimately overtakes the right. Pull back on your right, and you "trick" the lady into feeling that you are rotating on the spot, which means that she may move forward as though to follow a Twist. So remember: Move sideways strongly as you rotate, even if your step is smaller than hers.
The following step forward on the left foot has the same premise: Move directionally, and she can't help but follow. As long as you are moving forward, she will almost inevitably move back. The rotation necessary to achieve a left-side lead should not come as a result of pulling back on the right side; It should happen when the left side swings forward past the right.
This alone should be more than enough to communicate your intentions. But there is something else that I haven't mentioned yet, which will ensure a fool proof lead: Shape.
For the Twist, I would keep my shape rightward on 3, 4, and the first half of 5, all the way until the lady's RF brushes to LF, before leveling out and then taking my right side up and back in order to lead her to PP. That's holding the rightward shape a lot longer than you might expect, but it's very effective.
In stark contrast, I'd swing my right side up *as* I take my weight to my right foot between 2-3 of the T-mark, giving her a better swing towards my right side and allowing me a stronger progressive movement. If you shape after your weight has been transferred to your RF, it's too late. You must create this shape from the veering in of the left knee and dropping of the left hip while it still has weight. This may seem unusually early, but trust me... it's effective.
This is a lot of detailed information that may seem somewhat technical and uninteresting. But if you use it in the right way, I guarantee it will give results. Your first goal should be to understand it intellectually. If there's something that's confusing, feel free to ask. After that, your next goal is to apply it to your dancing, which will take much longer and will require the help of an instructor.
Good luck, and don't forget to enjoy your dancing!
Sincerely,
Jonathan Atkinson