Monitors will help, but if you're singing out of tune a little you will have to work on that a bit. Your voice will sound alot different with a pa system than it does just singing and playing the accoustic guitar. What kind of mic are you using? A cheap mic will give you nothing but trouble. What I do when I sing is get right on the mic. Put your lips right on it. Some effects allways help too. If you can't hear yourself in rehersals get closer to whatever speakers you are using or turn one of them towards you so you can hear yourself.