Do you have a mental hack, a playlist, white noise, etc?
I personally use a hand crafted Spotify playlist that works well, but I’m always looking for another trick to hold the flow for longer.
So far, this is the ONLY way I've been able to reliably get in the zone. It's crucial that I avoid Slack, email, or the web until well into the afternoon. Sometimes I feel mentally "fragile" for struggling to multitask or return to work after being interrupted, but if it works, it works. I'm lucky to be part of a team that isn't too keen on frequent meetings and doesn't expect instant Slack responses.
Also,
> Clean my desk completely.
It's amazing what having a clean environment does to productivity. After being more clean/neat in my life, I've found that clutter has kept a constant burden in my mind. Clutter just makes working/living less approachable. I mean this both digitally and physically.
Flow is usually something not to be sustained for long periods, because sustained flow is actually not practical - there must be an intermittent ebb to every flow state (usually in the form of breaks).
I noticed you mentioned Spotify and I commend that. Music makes everything seem epic even though you are doing very mundane tasks.
My only tip for making a flow state last longer is getting natural nootropics in your system like coffee, walnuts, omega-3 fish oil, MCT oil, and blueberries, which are all brain-boosting foods.
You do not get into a flow, you get into a rhythm of break - work - break - work.
There is a section of albums by “The New Law” which is a good place to start. The list is made to be listened to album by album so there aren’t many distracting transitions.
+ turn off all notifications
+ block enough time for uninterrupted work
+ write down all steps and goals before starting to work