For effective discipline, think about your favourite teacher in your own life and model yourself after that person. Chances are that your favourite teacher was firm, fair and consistent. He/she was a good role model and very clear on expectations for appropriate behaviour. Notice that no one says their favourite teacher was a "yeller", nor were they punitive.
To build teacher authority, follow through on your directions for doing things right, not just your consequences for doing things wrong. That way, you won't get a reputation for being punitive, you'll get a reputation for "meaning what you say" - and that's the foundation for authority.
Stress prevention. Almost all effective discipline is done before there is a problem, not after. Anticipate. Design the work space and lessons accordingly. Know which student work well together. Know which students are capable of working in groups and which ones need personal space. Make decisions based on insights, not incidents.
The number one prevention tool for teachers is student engagement. "Students who are engaged in learning are not engaged in misbehaving."
During lessons, use your voice to maintain the flow of the lesson. As much as possible, use non-verbal prompts and cues to deal with student behaviour. If it is necessary to speak to a student who is off-task, re-engage the student with a question related to the lesson, not with a critical comment that would interrupt everyone's learning.
Provide "sponge" activities to "soak up" idle time for students who finish quickly.
Just because a student hears your directions doesn't mean the student has registered the information. (Hence the old saying, "In one ear and out the other".) Get feedback from several students to make sure directions are well understood. Also, allow students to check with their "study buddies" for additional clarification.
Transitions make the best entries. When students come into a school building, ensure playground behaviour stays on the playground. Then, as students enter the classroom, ensure hallway socializing stays in the hallway. In other words, students should come through the outside doors ready to enter and the classroom door ready to learn. Remember that teachers must be at the doorways in order to utilize them as points of transition.
A trip to the Principal's office for discipline is supposed to be a promise of getting the intervention and support you need for behaving correctly, not just the consequences you deserve for behaving badly. Threats such as, "If you do that one more time, you'll be in the Principal's office" are the school version of, "Wait till your father gets home".
Almost every teacher has a positive view of school but many parents have negative memories of school. For many parents, school was a painful experience full of failure and social isolation. It takes time, effort, understanding and a lot of listening to build a partnership with parents who have never felt positively connected to the school system. Make them feel welcome and have discussions focused on building success for their children.