Some tips for #WhatsApp, the most popular messaging app today:
You can pin upto 3 chats from your favorite contacts to always appear on the top, swipe right on a chat or tap and hold.
You can set custom notification sounds for every chat just tap on the top and then select custom message tone/notification tone depending on OS.
You can use your WhatsApp on computer by either visiting web.whatsapp.com or downloading install-able client for WhatsApp, this does require your phone to be online to work.
You can quickly add filters to photos you send, after taking or picking a photo from your gallery just swipe up to quickly access filters.
You can just delete selective data from a chat, like if you want to delete all spam videos from a chat, to do this go to WhatsApp settings go to Data and Storage Usage and then Tap on Storage Usage at bottom to see how much each chat is eating up.