I recommend two "how-to" manuals: the best by far is "The Complete MG TD Restoration Manual" by Horst Schach (a very detailed installation description with photos), and "MG T Series Restoration Guide" by Malcolm Green. Not as good as the first source, but more additional information. Both are sold by Moss Motors.
I installed a Moss vinyl top on my 2-bow '51 TD following Horst's instructions. Some lessons learned: Make sure the bow frame is mounted into the same holes drilled by the factory hands (which is a challenge if you've just replaced the interior side panels). Have the side curtains in place to help fit the new top to the side curtain top edges correctly.
Horst's instructions are very complete, and I had no problem getting the vinyl attached to the front bow and the rear tub wood. It is a bit of an act of faith when you have to cut darts out of the front corners to get the fabric to wrap correctly around the windshield corners (start with small cuts and/or practice with some scrap material first). It makes sense once you see how the material goes around the corner. The hidem straps are easy to install.
Keep in mind that the material, particularily vinyl, will shrink a bit and be very stiff in cold weather. We've got several car club members who had their tops installed very tight with nary a wrinkle on a warm day, but they struggle mightily to put the top up on cold days! I used a warm-weather "relaxed" fit that may not meet concourse standards, but I can erect it when cold without too much cursing, and it's still there after 5 years!