How do you improve span of attention?

Assume you you are not unhealthy: psychologically,intellectually, medically, nor diurnally (day-night rhythms), you can use several methods. Like all learnt patterns, adhere to your traditional "alert" methods: time of day /night; furnishings, environments (alone /accompanied, quiet/ noisy, lighting, air conditions, etc.). Prior to the event, you may need to "prepare": mood-setting, bathroom needs, food-drinkr needs, interference-avoidance, blood-sugar & caffeine-timing & renewals to peak at the required timings. Rehearsal is best, since it is possible to be too alert, too peaky. In the actual event(s), normal body adrenalin can easily upset expectations. The placebo affect works well in all situations: self-hypnosis (self-talk) to delude yourself into a higher or lower alertness condition, as necessary.