As a former muslim and living in islamic country, i can tell you you can witness to muslims by strenghtening your faith and asking the guideness of the holy Spirit, and getting some knowledge of islam teachings pecially the lies in islam about christianity; none can tell you a step by step how to witness, because muslims are individuals and they differ from one to another, you can share with them and pray God open their heart and their mind, because God who convince people not us.
Jesus said go and spread the Gospel, to spread the Gospel is to know the Gospel and trust in God power on transforming people, and pray for them, not everyone who you witness to will accept the truth, because they are poeple hardened their heart, and they are people that can be open and God is working on them.