a) Push notification fatigue b) Lifecycle of push notification c) Push notification open rates d) etc.
Curious if any tools/processes that have been tried, what worked/didn't work.
a) Push notification fatigue
You should treat notifications as you do any other major product feature. This means seeking to experience the feature yourself as a user would, doing user research & interviews, and instrumenting analytics around this.
In general, you should make sure that notifications are very useful to your recipient as often as possible. For notifications that make a vibration/sound, aim for 50%+ of notifications to be very useful. For notifications that do not play a vibration or sound, 20% is a reasonable target.
b) Lifecycle of push notification
Tools like OneSignal help with this. We recommend setting up a well-thought-out series of automated messages, or scheduled messages, based on user interactions.
c) Push notification open rates
OneSignal and other tools provide this data. Keep in mind that open rates are just part of the picture -- users often open the app directly after receiving a notification. In OneSignal this is tracked as an "Influenced Open". Furthermore, make sure you're tracking CTR against notifications actually received by the device, not just notifications you send (Some notifications may have been "sent" to devices that are no longer active and won't receive it).
Whether you use OneSignal or build notification support yourself, this is an important metric to instrument correctly and keep an eye on.
For example, you might follow 100 people on Instagram, but only really care about updates from 20 of them. Instagram uses several signals to detect which people you want to hear updates from (such as whose images you favorite the most). It's impossible for them to always be 100% certain, but they do the best they can. I'd wager that about 50%+ of the Instagram notifications I get are those I feel are worth clicking on, and I'm glad they send them to be.
There are solutions like clevertap that might solve some of those issues. I think having granular level approvals would help. I turned off most news apps notifications because they were spamming with tennis results and royal weddings etc... when in fact I would appreciate more relevant content to me that they could easily have seen from my consumption patterns within the apps like breaking tech news etc...