Start by measuring band against the length of your lid and trim to fit. If the lash is too long, it will irritate the eye, causing it to water and the lashes to lift.
When you're happy with the length, apply a layer of lash glue to the lash band and wait roughly 30 seconds until the glue becomes tacky.
Using a pair of tweezers lift the lash in the middle and anchor it to the centre of the lid, as close to the lash line as you can get without sticking to your own lashes. (If the glue slips and slides the glue wasn't ready to attach yet)
From here you can fix each side of the lash down to fit onto the lid comfortably.