Set your account to private by making your phone number and email private in Snapchat settings
Go to Settings > Privacy Controls > Contact Me and set it to My Friends
Go to Settings > Privacy Controls > View My Story and set it to My Friends or Custom
Go to Settings > Privacy Controls > See Me in Quick Add and turn it off
Go to Settings > Privacy Controls > Location and enable Ghost Mode in Snap Map
Go to Settings > Privacy Controls > Memories and choose who can view or save your content
Remove people you do not want as friends
Only accept friend requests from people you know
Turn off notifications for unknown interactions if needed
Use a strong password and enable two-factor authentication
Review connected apps and remove anything you do not trust
Limit who can message you by keeping messaging restricted to friends
Hide your story from specific people using Custom Story settings
Avoid sharing personal information on your profile or snaps