Finding the zone.
It's there, you don't even need a road map. Perhaps just a reminder or two of the general direction.
Surround yourself with creative things which inspire you. A piece of corkboard painted flat white to which you attach an ever-changing exhibit of inspirations is a good thing to have right above your work space. If your work space is the kitchen table, use a table easel to hold the corkboard. A piece of string suspended between two discretely placed hooks and draped with a white sheet can cut the mundane clutter from your field of vision.
Wear spceial clothing. I actually have special clothing which I wear when I am making art. Not a paint smudged smock, altho' that becomes the stereotype. The smock was traditionally the uniform of the farm worker. It's ample sleeves and large size allows for free and unencumbered movement. The beret? If it works for you...
Have a special food and beverage close to hand, unless you work with poisonous pigments. (sometimes I do...) And yes, absinthe which contains real wormwood when served over ice does indeed stimulate the creative synapses in your brain. As does chocolate.
Listen to the music that brings you there. Listening to music which is new to you can get you out of the rut of doing the same old same old.
Have you assembled your tools, materials, media? Sometimes just handling my tools is enough to move me from questing to creating. I love my paint. I love to look at the colors. Instead of a fixed palette, I use little pans for my own watercolours so I can arrange them in new groups and families.
Be generous with your creative self. Buy two pieces of that special paper, stretch two canvases, prepare to bead two necklaces instead of one. Sometimes the creativity spills over into new and unexpected work, and it's wonderful to be ready for it. And you will not fear to "make a mistake" if there is always the opportunity of starting over.
Take a break when you need it, and also keep interruptions at bay. I turn off the phone when I am working. Keep it flowing.