At risk of sounding like a bit of a design wanker i thought i would share my philosophy on design and creativity now that i’m 50 years old and have been a designer for lots of years probably 25 or more years. i have designed everything from toilets and desk “furniture” to airline interiors and luggage.
I'm a product designer so some of these principles may not be applicable to graphic designers / app designers etc. But you will get the idea. I'm sitting down in multiple sessions to put this list together, i'm sure i will re-visit it and update it from time to time.
Make it do more than one thing
Don't force it but if adding a little clip here or an eyelet there you can dramatically improve the functionality of the object then its worth it.
Surprise people
Hidden pockets, a surprise free dust bag. Well considered feet designed to keep the bottom of the bag clean
Don't overcomplicate it
Keep the design neutral enough to allow people to put their own stamp on the product. Eg. the internal pocket structure of a bag or a modular system for furniture allows the owner / user to further customise the product, adding a personal value to it.
Make it accessible
Products designed for access for people with arthritis benefits people who don't have arthritis. Wheelchair access on curb sides allow bicycles, buggies, prams and scooters to also use this path. This is called the 'Cut curb effect' The phenomenon of disability-friendly features benefitting and being used by a larger group than the people they were designed for. In the world of bag design i was surprised to find that if i make the back base of the backpack straps unclippable, then they can be clipped over the back of wheel chairs and walking frames. When i design straps for bags to attach onto bikes, they can also equally be attached to baby buggies and wheel chairs.

Think further than just the one product
You might want to add some styles to the range in the future. So its good to think of your design in the context of either an expanding family or even in the setting where it is going to 'live'.
Use the best materials you can afford
The cost for making bags is in the labour, so when i design i try to use the nicest materials, hardware and components than the product can afford. This includes quality zips, quality buckles and other functional elements that can break, will break, so to save yourself from reading angry emails from unhappy customers, just firstly try to design with the least amount of items that can break or go wrong and second to that, use high quality components.
Use what you've got
If you are making something at home for example craft items or trying to fix something with a hacked up product in the house, i like to challenge myself to use what i have already. This sustainability philosophy definitely lays in the 'reuse' segment of the 'reduce, reuse, recycle' order of being more sustainably minded. When i am designing a bag for example, i would use the same lining for all the ranges, fabric waste is a big problem in manufacturing and by not having different designs for different bags you can get the most out of one more iconic, recognisable fabric. The advantages then is that 1) you can invest in making your brand more recognisable, reduce costs and be mindful of the environmental impact at the same time.

Don't get paralysed by perfectionism
With the fear of being labelled 'slap dash jacqui' i cannot emphasise how true to this point i practice everyday. Evening when i'm cleaning the bathroom its a matter of 'good enough for now' attitude. If i had to hold myself to a perfectionist standard every time i go to clean the bathroom, i don't think i'd ever do it. This same attitude translates into design and marketing my brand Goodordering.
Have fun, Its not brain surgery
Don't take design too seriously, don't labour over it. There is a difference well considered design and designing something within an inch of its life.