After some time your fret hand will know just how much pressure to use, before that point your fret hand needs to develop strength so you can last the distance. Also consider how high the action on your guitar is cause if it's too high you'll be using far too much energy fretting those strings. An acoustic guitar is obviously harder to fret than an electric and keep in main that even seasoned pro's play acoustic will suffer after a long play barre chord song. Check out the barre chord songs to practice on at www.nofretguitarlessons.com.au