Even seemingly innocuous language can promote gender bias. When addressing the class, for example, avoid saying "You guys," which favors boys. Instead, use a gender-neutral term such as "people" or "gang." Encourage your students to use "he or she" when giving examples. If they slip up, don't chastise, but use it as an opportunity to discuss how gender bias invades our language. Similarly, make sure that examples in your lessons alternate between genders. If you are using an old textbook that only uses "he," point it out to students and have them correct the textbook.
No matter what age-group you are teaching, make sure that group work is done without gender separation. Never divide students based on gender. Sometimes, especially in certain age groups, students will tend to divide themselves according to gender. If this is the case, intervene and mix up the groups. Similarly, if you allow students to choose where they sit in the class, don't allow self-selecting gender homogeneity to take place on its own.
It is every teacher's privilege, especially at the elementary level, to assign jobs to students. Make sure you don't discriminate based on gender. Don't give jobs cleaning up exclusively to girls, and jobs carrying things exclusively to boys. If you need a few students to carry a box of books to another room, make sure you ask both boys and girls to help. If you are doing a unit on cooking or parenting, make sure you get boys involved in volunteering.
Teachers can sometimes unwittingly create different expectations for boys and girls in different disciplines. Be conscious of this and make sure that you hold girls to the same high standard that you expect of boys in conventionally "male" disciplines such as math and science. If you are teaching physical education, make sure not to allow boys to play rougher sports while excluding girls from the competition. Discuss your expectations with the class and make it clear that gender will have no bearing on them.