to be honest i very rarely get low motivation days unless im not well and even then i normally get out and work!
obviously as you get older you WILL get responsiblities,bills to pay and holidays to pay for and evenings out at nice restaurants,nice cars,clothes etc.
i usually get most of my work cleaned in 3 weeks a month so it allows me some chill out time before next months onslaught.i also work in most weathers so i very rarely get behind these days.
also when you have a good round you dont want to get behind because you get used to a certain lifestyle and enjoy making money and dont want to let your customers down.
being ultra organised with worksheets,invoices printed,round software and decent carbon poles all help as well.
look after yourself helps.eat decent food(if you can afford it!).keep boozing for weekends if your a drinker and give up smoking if you do.
if your having trouble motivating yourself ask yourself why?self motivation needs to be strong when you work for yourself if you want to be successful.
best wishes
dazmond