Disable Last Seen and Read Receipts aka blue ticks
By default, WhatsApp lets everyone know the last time you used the app. Your last seen timestamp, profile photo and status message can be toggled between Everyone, My contacts, and Nobody in Settings > Account > Privacy on both iPhone and Android.
Read Receipts, notified by those Blue Ticks can seem too obsessive and creepy. You can disable them too, but that also means you wont be able to see read receipts from other people.