Guides
Written to be read once and used, rather than skimmed. Where the honest answer is “it depends”, they say what it depends on.
The best time to post, and why the tables are useless
There is no universal best time, and the published tables are measured on somebody else's audience. Finding yours takes about twenty minutes.
Aspect ratios and safe zones
Five ratios cover everything. Getting the ratio right stops the crop; getting the safe zone right stops the interface eating your text.
What hashtags actually do now
They stopped being a distribution channel and became a labelling system. That changes what they are for, and how many you need.
Your reach dropped: how to work out why
Almost nobody is shadowbanned. Work through these in order — the answer is usually in the first three.