No special posture or equipment is needed, just an ordinary chair or cushion that allows the body to sit easily upright and alert, comfortable but not too comfortable. The spine stretches up from the base right through to the top of the head even to a sensation of reaching above it.
An alternative to sitting for long periods is to stand up against a wall, not leaning against it but just touching all along the back of the body from the heels to the head. This provides both a guide to perfect posture and a means of feedback from the body, in particular barely discernible micro-movements of the head that can be quite intense to discover. One can alternate sitting and standing in this way to break up any feelings of monotony.
The eyes have it. The usual mindfulness practice is to focus on breathing as the link that bridges mind to body. However attention to the movement of the eyes can also open the portal to thinking. Crowded thoughts, quick eyes and shallow breaths are habitually cued up to follow in a cascade one from the other. So look to the eyes as they look out.
It will be tempting to chase and catch the butterflies flitting around your mind but more productive to just watch as they come to land.
Away from our homes forests and other sacred spaces are natural places to sit still and listen for a while, particularly in the morning before eating. Thirty minutes to an hour can easily pass in the quiet observation of both mind and nature.
Make it a priority to have space and time to sit quietly in the shadows and come to the light by sipping a tall cool glass of silence, all at once or throughout the day.