As developers this is challenging since so many of our tools require network access. I've had minimal luck with various site blockers since you can always just disable them. So here's my plan:
1) Prepare. Download documentation you will want and invest in dead-tree copies of relevent books.
2) Have 2 desks, one with your computer, and one without. I physically move to the non-computer desk for design work and thinking, then get up and move to the computer desk to program. A comfy chair for more creative thinking is a nice addition to this setup.
3) Make it really hard to turn the internet back on. When I started this I would actually go and put the modem outside in my car to make it annoying enough to turn the internet back on. As I've gotten more comfortable with this practice I find it's enough to just go and turn off the modem, but I've found that simply turning off wifi on the computer is not enough distance.
Sounds extreme, but by seeing how much work I need to do to disconnect has taught me how much of an addict I really am and given the motivation to work on the problem.
Through this process I've gained a new level of respect for Emacs. The built-in documentation browser is amazing, both the tools for browsing and the quality of the documentation. I'm able to figure out everything I need to about Emacs without touching the network.
This also makes me want to put a lock on the refrigerator that can only be unlocked by running a certain distance on a treadmill. LOL. I have to create artificial grit, I don't have an overabundance of the natural kind.
Go to the beach for a couple of days to get a groundbreaking work related idea.
I find I'm quite mentally creative when doing tasks such as cutting the grass, which I don't find tedious, but instead require a sort of process-control mental activity. I actually enjoy cutting the grass for its physical side combined with the opportunity to get a good looking result from a task that takes about an hour. Hoovering doesn't inspire the same mental creativity.
To me mowing the lawn is an activity where my mind can disengage apart from watching for the occasional suicidal squirrel - while vacuuming is an activity where my brain is constantly on the watch for something being amiss and me accidentally chewing up an expensive cable or rug.
This all aligns closely with what I think the distinction is for tasks that allow you to be creative - something relatively straightforward that requires your hands to be busy but where you can mostly zone out. For this purpose I like eating "slow fruit" namely pomegranates and grapefruits - where I take both fruits apart laboriously by hand after peeling them (eat the grapefruit like an orange - but peel each slice). While I'm doing this my mind is free to do whatever and my hands continue with only minimal guidance.
Kinda similar to how I use my gym membership ;)
It's also best done without the pressure of "I must come up with something". Sometimes there really is pressure and I have to spend some time to trick myself to build up momentum.
I like to schedule time to go on a 30 minute walk with my phone in Do Not Disturb mode.