Choose a blind to fit the width of your window frame. Measure from each end to the blinds fixing points, so you can transfer those measurements onto the wall above your window.
Next measure up from the window and mark out the position you need to screw the fixings evenly on each end and the middle.
Starting with an end fixing, take your drill and screw through the eyelet on the blind, straight into the wall. Attach it loosely so you can swing the blind up and screw in the other end. Leave attaching the middle fixing to last.
Before you tighten all the screws, check your blind is level with the spirit level. Then secure the blind in place. Make sure that the chords are out of reach of children.