Assalamu alikum, Hazrat Muhammad PBUH first show from his behaviour than after the age of 40th he started preaching to non muslim that there is no GOD worthy to worship except ALLAH.the most effective way is to first completely follow and fulful all obligation specially behaviour with other means, relation to friend,relative,how you work beautifully,how do you meet other,helping other without any condition and expectatoin means just for ALLAH,hospitality,and honesty in any relation than you can certainly convince any body.practicing islam is more influential and as far as Hidaya is concerned that is only in the hand of ALMIGHTY ALLAH.you are the representative of islam people first see you and your chrismatic personality according to sunnah can help you.ALLAH SEE YOUR INTENTION AND EFFORTS.MAY ALLAH HELP YOU IN THIS PATH.ALLAH HAFIZ