To prevent common disruptions in the classroom, state your preferred ways of dealing with them during the first class session at the beginning of the term. Include these preferences or rules in a written syllabus. For example, you may have a policy for how to deal with bathroom breaks during lecture time. Clearly state in writing that you allow students to get up and leave the classroom at any time if they need to, or that you have a "locked door" policy so that if a student leaves midclass he isn't allowed back in. The policy you use is up to you; the important part of the strategy is making your preferences clear from the beginning.
In some cases, the best management technique is to pull aside a student for a one-on-one talk. Do this if a student has poor hygiene that is distracting you or other members of the class, if a student sleeps or is disruptive in class, or if a student is repeatedly tardy. Be sensitive to possible cultural differences regarding hygiene while making clear that it's a distraction to other students. One-on-one talks help you understand whether an underlying reason explains the student's disruptions, can offer a way for you and the student to come to an amicable solution, and can show the student that you are concerned for her well-being.
Maintain a culture of respect for yourself and your students, and expect that culture to be practiced by all students. Begin by making it clear in writing and through your actions that each person in class has an intelligent contribution to make and is expected to participate through discussions, projects and assignments. Model that respect by taking comments and questions seriously, so long as they're asked with the proper intent. Do not tolerate aggression, sarcasm or condescending attitudes toward you or other students, and dismiss from class students who behave inappropriately.
When in doubt about how to manage a particular situation, read your faculty handbook to see if the issue is addressed. Most colleges and universities give faculty a handbook shortly after hiring or at the beginning of each school year. Basic management techniques might be addressed, and certainly techniques and steps for handling dangerous, sexual or physically harmful situations will be discussed.