Question: I've got an older iMac running macOs Mojave. It is terribly slow and I am interested to see if we can improve the performance. Can you recommend steps to consider to improve the performance? 

The performance issues I see impact the operating system and all applications. It's not specific to a single app.

When viewing the About modal:

* MacOS Mojave Version 10.14.6 (18G103)
* iMac 27-inch, Late 2012
* Processor: 3.2 Ghz Intel Core i5
* Memory: 8 GB 1600 MHz DDR3
* Graphics: NVIDIA GeForce GTX 675MX 1GB

Looking at the System Report, I see:

* Status on Memory Slots is OK. Has 2 4GB 1600 DDR3 cards.
* Hard Drive: I have about 500GB of available storage on 1TB hard drive

Other than these basic stats, I'm not sure what would be relevant to help diagnose the performance issues on this machine. What information could I provide to help determine the issue? Thank you.

Answer: 
The only two things you can realistically do are change the HD to an SSD & upgrade the RAM.

Some iMacs have GPUs that can be upgraded [slightly] but that's not really going to gain you much.

A 1TB SSD can be bought these days for the price your 1TB HD would have cost back then, approx $£€ 100.  

According to [Everymac](https://everymac.com/systems/apple/imac/specs/imac-core-i5-2.9-27-inch-aluminum-late-2012-specs.html) that model can take 32GB RAM. I'd recommend at least 16GB these days. 

The SSD alone will put some spring back in its step. The RAM will let it breathe a bit better.
There are basically two things you can do:

* Get more RAM. There are two free slots, so adding 2x4 GB is easy and having 16 GB instead of 8 GB will make a difference
* [Replace the drive](https://everymac.com/systems/apple/imac/imac-aluminum-tapered-edge-faq/how-to-upgrade-imac-hard-drive-aluminum-2012-2013.html) with an SSD

I have a late 2012 Mac mini as my main machine, with 16 GB and a Fusion drive. Definitively not the fastest machine but useable, even with big RAW files etc.