Hi I have used Mylar for making sails. Use a good quality double sided adhesive clear tape, like selotape for sticking panels together, but be careful you get just one shot at it. If sticking a long length have a flat surface and if you can work from the centre outwards taking care not to put any tension on the adhesive tape as it will curl the sail. It is worth checking on the Internet as the straight part of the sail going up the mast is actually a very shallow "S".
Where you have any attachments, hooks, ropes, eyes, then strengthen the area first.
For the corners of sails I cut a circle of mylar and cut out segments that fit the corner. Apply the adhesive tape and discard surplus and stick on the sail. For hooks etc up the mast I cut these in half circles and apply as before.
The very small eyelets can be obtained from Sails Etc, together with a small punch to suit size. It is all very easy just needs patience and accuracy. Be careful when cutting main sail and get the large angle right, it s usually a bit less than 90 degrees or use old sails as patterns.
I use scissors to cut with following a feint pencil line and a compass to make circles, the point telling exactly where the centre is for cutting segments.
Good luck
Roy