MultiplyChances to Engage
Let back-end learn about the user.
If available, use back-end to gather information about the user to reinterpret into what the user will want to see.
Cater meaningful content.
Provide contextually applicable content to maintain the user's interest. This will make users feel the system works and their actions are interpreted into what they see.
Timing is imperative.
Follow a general path of though to appear just when user comes off the last engaging content. Experience must be continuous.