What helped me improved in this area is start thinking about the diplo setup from beginning
This is very good practice
You should make plans for AIs as early as possible.
To add on my initial post, while I will maintain that you can monitor how aggressive the AIs are likely to be depending on how much empty space there is,
I do not recommend to systematically plan for a HBR rush.
I think it's one of the strongest rushes in the game BUT
Most of the early game is about getting edges and, especially, a tech lead. A tech lead amounts to a gigantic discount on military units.
And it doesn't always happen that a rush is profitable vs teching up + invading easier.
A properly set defensive war comes on the cheap. This is an entirely valid option. Repelling an 8 units stack with 5 and then suing for peace while you're pursuing Lib is probably gg. This does require some awareness of the danger, though, and I would think everybody's been caught before
In the cost-effectiveness sense, I do feel a little uneasy with the Construction wars (unless 100% boxed in) and acknowledge not all targets are adequate for Horse Archers.
A costly offensive war in the BCs, I would generally not consider as desirable.
If we push the argument forward that plan N°1 for the player is to get a tech lead, I mean,
Bribes...
They're a lot more efficient if you have military of your own but they're a very good way to completely own the warmongers. Provided you can afford the bribe, bribes can be very expensive if you are not at war yourself.
There are the Gwaja's all warmongers maps to testify for this one. Absolute Zero also loved to do that in his days. I do not diplo much and that is my fault but diplo is wide.