Hide Your Last Seen Time
By default, WhatsApp show your the last time you've visited the app. But WhatsApp also provide a feature to hide your Last seen Time. To enable it head to Settings > Account >Privacy, and Tap on the Last seen, and change the option to Contacts or Nobody.
Add a Shortcut of any chat or group chat to your home screen
Hold a press on a group or chat to open the menu, and select the 'Add Chat Shortcut' option. That's it.
Save your Data by disabling media from auto-download :-
Go to Settings> Chat settings > Media auto-download, and specify these options in Mobile-data, Wi-Fi, and Roaming.
When your Message has been read
Long press on the sent message, then select the (i) Icon to when was your message has been read.