I recently taught myself how to play the bass. The most important thing was to learn where each note was on the fretboard.
For the guitar, I think it might be helpful to start by memorizing the hand positions for different chords, and practice moving between them. Just google guitar chord chart and I'm sure you'll find lots of help.
For me, it really helped once I got a handle on things a bit to play with a band, or to get some chord sheets and play along with a song. If your church has a worship team, you could see if they would mind you coming to practice and playing along with them as they practice.
Beyond that, you have to find out what works for you, don't get discouraged, and just do it.
"I do not seek to understand that I may believe, but I believe that I may understand: for this I also believe, that unless I believe I will not understand." --Anselm of Canterbury
For consider Him who endured such hostility from sinners against Himself, lest you become weary and discouraged in your souls. You have not yet resisted to bloodshed, striving against sin.