Do you feel you can sing the song accurately? If it were me, I would start by singing and holding the first note and then fingering different notes on the guitar until you find the right one. It should be obvious when you hit it (and also if you are under or over pitch). After you do that with a few notes, you'll probably be able to idenify the key and scale/mode the song is in (if you haven't already identified the key using internet resources). If you know the key and scale, that will narrow down the range of likely possibilities for the notes. The 7th and 8th notes should be easier than tne 5th and 6th notes which should be easier than the 4th and 3rd, etc.