Old age, sickness and death are good choices along the lines; 'Today effort should be done; life is uncertain, death is certain. Youth is a fleeting, unreliable and death might overtake you before you finish drawing a breath.'
Reflect on the drawbacks of laziness perhaps like this; 'Laziness is looked down upon by the world, lazy people don't accomplish even mundane tasks let alone the ultimate goal'
Reflect on the danger of not finishing your work, perhaps like this; 'Were i to die without finishing my work, it would be to my detriment, a cause for regret, a cause for birth, aging, sickness, lamentation and death...'
Reflect on the good fortune of being able to practice; 'Truly many would envy me, those beings in hells and those unable to practice this good Dhamma, how truly fortunate am i being blessed with an opportunity window in this very moment"
One can consider the words of the Tathagatha; ~ 'Practice jhana monks, do not be negligent so that you don't regret it later' or ' Just as when a person whose turban or head was on fire would put forth extra desire, effort, diligence, endeavor, relentlessness, mindfulness, & alertness to put out the fire on his turban or head; in the same way, the monk should put forth extra desire, effort, diligence, endeavor, relentlessness, mindfulness, & alertness for the abandoning of those very same evil, unskillful qualities.'
Furthermore one can consider that it has been said that;
(386) The sun shines by day. The moon glows at night. The warrior shines in his armor. The brahmin shines in meditative absorption.
or you can consider that there are two modes of practice; 'A painful practice' and 'A pleasant practice'
Considering the drawbacks of the painful and the benefit of the pleasant practice, it is possible that one would resolve on the pleasant development.
There are other things one might want to give attention depending on the particular hindrances you are facing, ie reflecting on unattractiveness & drawbacks will counter infatuation, reflecting on the benefits of wakefulness and the drawbacks of sleeping will rouse energy.