Well, it was over ten years ago that I did the Midget top-yours should be permanently attached at the back by that chromed trim strip with snap fasteners on it, correct? I seem to remember starting at the back, making sure that I had all the Tenax fasteners lined up and marked for their holes, then attached that trim strip. I've no idea what sort of measurments are needed-if you have your old top still intact, measuring the locations for all the holes and Tenax fasteners (those fasteners around the edge of the top, you pull up on a button to release them) before trying to mount the new top would be a good idea, then double checking them after it's attached (and before you cut any holes!). After attaching the top at the back, I did the front. The top's held in by the aluminium piece that holds the rubber header rail seal-the ally bit's held in with pop rivets, and screws won't work for this application, so if you don't have a pop rivet gun and some small-ish rivets, stop reading, jump in your Midget, and go over to Sears and buy one (they're not terribly expensive, and can be useful elsewhere). Once you've attached the top up front, and have the rubber strip back in (I just popped mine in there for this step-when you're truly done it helps to glue it in with something-I forget what I used), put the top up and latch it at the header rail (NOTE:at this point you should not have any of the Tenax fasteners fitted yet!). Roll up the windows and take a look-does it fit okay around the windows? Is there obviously a gap around one side window and more than enough material around the other? Then the top's not lined up correctly and you have to start over. The beauty of it is-the holes you need to punch for the attachments at the header rail and at the back under the trim strip are hidden, so if you have to do it again, nobody needs to know. NOTE: don't Swiss-cheese it and put thousands of holes in the top just to get millimeter perfect alignment-you stand a good chance of weakening the material! After you get things lined up, you can put in the Tenax fasteners. If the holes you marked earlier (you did mark them, didn't you?) still work, go ahead and install, otherwise re-measure.
Hm, one final note, out of order of course, is the snaps INSIDE the top-those straps that hook onto the top frame, and the snaps that go to the winshield frame. These should be installed before you put the top on. Use your old top as a pattern, because even if the top's not exactly lined up like the old one, there's an awful lot of wiggle room for these. My only other tip is to do this on a nice hot sunny day out in the driveway. It'll make things a bit sweaty and unpleasant, but will make the top material nice and soft and pliable, and it's easier than trying to use a hair dryer to heat things up.
Good luck!
-William