I'm a crazy person. I like bright, bold colours and have a slight obsession with animal print (zebra and leopard in particular) and that's very visible in my flyers and cards. Make it fun. There is nothing I hate more than washed out, plain ass flyers (that being said, personal preference is a thing). Make it eye-catching.
Simple flyers are easy enough to do up. Just throw some pictures of your products on the page, shop name, logo, slogan or description of what you sell and BOOM you're done. My previous full-page flyer had larger images and was purely HF, but this time I decided to make half the page dedicated to promoting my blog. When I send out an order, I print the invoice on the back of the flyer. Handbills (quarter-page flyers) should have one or two images, company name, and web address. Simple and straight to the point. These two are easily and cheaply printed at home. When it comes to business cards, I recommend using Moo. They have great prices and a lot of options.
My business cards were all printed through Moo. I've also got some of their mini cards which I use as tags when packaging pouch and clutch orders. Probably my favourite thing, though is their stickers. When I first launched my shop, I ordered circular stickers as my return address labels, but I just ordered more with my little hound logo and the web address on to include in orders (and stuck one on my laptop).
Hope that helps (assuming you need the help). I've still got quite a lot to learn, but that's I've learned so far. I had initially planned on talking about how super awesome and fantabulous I am at graphic design with flyers and business cards (which I clearly am, look at this shit! :P) but my mind wanders.
Use coupon code RIOT10 for 10% off at Hellhound through the month of August. :)