One way is to get out there and do it, you learn a lot from your mistakes.
You also learn how little you know about the bible, how easily your faith can be shaken.
You learn humility and patience.
Then you get on the internet and download everything you can find to read and listen to.
Or you could do it the other way, you learn how to do it and then go out, but so many times people never go out, they pray for God to send people to them.
My advice; Get on your knees, not to ask if you should do it, but to ask for courage, a word compassion for the lost and passion for Jesus.
Then get reading your bible cos that's where wisdom comes from.
And make sure you're living the life you will meet workmates, old schoolfriends, neighbours, people who pick up their kids the same time as you, they'll spot a hypocryte if you are one.
Can I recommend Mark Cahill's teaching 'being a light in a dark world' it's excelent, find the wayofthemaster radio and listen to Todd Friel and Ray Comfort out on the streets.
There is a right way to do it and a wrong way but don't let that stop you, if your in a right relationship with God then put some trust in Him, he'll give you plenty of rejections to put you in your place, and encouragement to keep you going.
Listen to 'I got off at George Street' if you want to know what persistance is. People will ask what fruit you are getting but point out to them that the visible fruit is the change in you, not the amount of people who listen.
Also have a look at other threads on this site, there are a few now on this subject.