This is the Strings and Stringing forum...it's just fine to post your question here...
In normal "rest" position, the arm is at about 10:00 or so. I leave it there, slide the string into the linear gripper, but leave enough slack so that there isn't any tension applied on the string until the bar gets past vertical...tension starts getting applied to the string when I hit about 1:00 or a bit past that.
Let the arm fall gently to put tension on the string. If it goes past the horizontal mark, then lift the arm a bit and let it fall again...it may take one or two tries, but I usually get it on the first drop, or with one adjustment once I'm into the racquet a few pulls. If it's just a little bit short I can usually get it to settle at horizontal with a gentle "bounce/tap," but I'm stringing gut and multis, which are pretty flexible.
If you end up short of horizontal, release the string from the gripper and start again. You should be able find the right place to start (enough slack) after one or two pulls so that it becomes easy to get to horizontal or a little past it on the first pull, then you're home free.
I haven't done polys, so don't know about special conditions there...