A storage for your ideas
When I run out of things I want to draw, I usually ask a friend to suggest subjects. The problem with that approach is of course that after a certain amount of questions, that friend is going to be annoyed.
After completely depleting your social resources like this, further help can be found on the internet in the form of idea generators that you can keep clicking 'Next' on...
Both these approaches have one major flaw - neither your friend nor your random internet bot know what you actually 'want' to draw.
You relax by drawing Manga? A suggestion for a still life won't be much help then.
You enjoy pet portraits? Forget about that fantasy list suggesting Goblin warlocks.
Only you can tell what you really love to draw, and what you did just because you felt like it that one time. Your past behaviour can be a really good indicator for what might help in the future.
But how do you remember all those ideas? Here's a suggestion: Put them in a jar.
When you need inspiration, go to your jar and pull out a subject. You can't click 'next' on your jar, and you won't want to. After all, you have added subjects that you always enjoy.
How to make a jar of ideas
Make a list of all those ideas that keep popping up in your head - and take your time building that list; nobody's rushing you, and you don't want to add 'bicycles' just because you're watching the Tour de France right now and this is your one time per year that you actively think about this type of vehicle.
Keep your ideas simple - this is an exercise that is intended to get you going, not a thorough analysis of your theoretical masterpiece.
Once you have your list, all you need is a pretty jar, some coloured pop sticks, and some paint to mark them. The reason you will want to buy coloured ones is that painting them individually takes a lot of time. And this is an exercise to help you beat procrastination, not encourage it by decorating your sticks in a nice way.
The more ideas your jar holds, the more useful it can be to you.
But make sure to weed out sticks that don't spark creativity. If you have replaced a stick the last three times you pulled it out, it's time to get rid of it.
To get you started on your own jar, here's a list of what I've put in mine - remember to only copy those topics that actually spark your creativity.
Settings - a library, a coffee shop, a circus, a backstage area, a lighthouse, a kitchen, a labyrinth, ...
Characters (not gender-specific) - a mage, a thief, an artisan, a pub owner, a falconer, an inventor, ...
Random things - spices, lamps, marbles, playing cards, ...
Other topics: landscapes, authors whose books inspire me, ...
If you do make your own jar, let me know how it goes - and share some of your own topics in the comments if you want!