1.

Follow（often used when referring to social media）
关注(常用于社交媒体)

2.

Enroll (frequently used when someone joins a class)
注册(经常在某人加入一个班级时使用)

3.

Enlist (used when joining the military)
登记(参军时使用)

4.

Take part in(something) (refers to joining some activity or event)
参加某事(指参加某项活动或事件)

5.

Team up with (join a person or group in order to work together)
与(某人或某团体)合作

6.

Associate with (loosely joining with others in order to work together)
与…交往(为了一起工作而松散地与别人交往)

7.

Come aboard (commonly used when one joins an organization or business)
加入(加入组织或公司时常用)

8.

To network (when people try to meet others in order to join or associate with them in the future)
社交(当人们为了在将来加入或与他人交往而试图结识他人时)