tip no.1: Avoid automatic stuff. Simply manually shift stuff that sounds off tune or generally "not right" (excessive vibrato, non-stable held notes, non-perfectly singed short notes - all that stuff is relatively easy to repair by hand and almost impossible to find automatic settings for). It may sound like a lot of work, but finding the right auto settings arguably takes even longer.
Nevertheless knowing the scale of the song helps a lot, cos' that way you now which notes suppose to be (and not be) in the song.
Scale of the song can be found in several ways... Usually a song ends with the base note and chord and determining between mayor and minor is pretty obvious. Simply listen to the last chord and last note in melody in the song. Works 90% for folk and classic (our brain even expect it to be there and it it isn't the end of the song sounds "weird" or "unfinished" in many cases).
Another way is to look at the notes/tab/midi and write down all notes that are present in the song (usually analyzing part of the song is sufficient) - like the melody contains D,E,F,G,B# etc. Create midi file and put those notes in there into a single "chord" (transpose them into the same octave). Now put in the basic layout of minor/mayor scale (whichever is the case, I recommend filling two octaves on top of each other) - CDEFGAH for mayor or AHCDEFG for minor. Now shift this "scale chord" up and down until all the tones from the song fit into it - once that happens you've found the scale. Sometimes you find the song doesn't fit any standard scale (maybe the scale changes across the song or contains some "dissonant" tones or the song is in some weird nontraditional scale in the first place)... that doesn't obstruct you at all, because you've already found which notes it contains and which probably not - which is actually the reason why you're searching for the scale in the first place.