If I may jump in here:
For most of us, tapered leaders are an essential element in single-handed fly-casting. The idea is that gradually reducing the diameter from the front taper of the flyline to the tippet transfers energy properly for correct fly turn-over and for delicacy of presentation.
The butt section of the leader (Juro's 60%) should closely approximate the diameter of front taper of the fly line. From there, the middle portion of the leader stops down quickly until a small enough diameter of leader is reached to bend on the tippet section. The tippet then takes up the final 20%.
I'm impressed that you can cast a level leader at all, nevermind the hook to the left. You'll find casting a tapered leader much easier.
Some confusion may have arisen over the practice of many Spey casters of using level leaders (leaders of the same diameter throughout). While it may not matter (to some) in Spey casting, a tapered leader really does matter in single-handed, over-hand casting.
Try to use a "practice" fly. This can be a bit of yarn, as Juro suggests, or a fly with the hook broken off (these are easy enough to get if you fish anywhere near rocky banks). Having the fly on the end of the tippet helps you practice correctly and prepares you for the real thing on the water.
Getting back to leaders: look up the various formulae on the web. Note the creators remarks on brand names and relative stiffness of the leader material. This all makes a difference. Fluorcarbon tends to be of smaller diameter than conventional monofilament; so, if the leader formula you want is given in pounds or kilograms test, you must take that into account.
I prefer a stiff butt and taper portion; the tippet's limpness will vary with the species and conditions under which I'm fishing. Others will have different preferences.
On last thing: remember how you achieve that left hook! Sometime you might find yourself on the Gaspe dry-fly fishing for salmon, and being able to throw a upstream curve can be a real advantage in presentation.