Honestly to me the hardest part about making graphics is finding the perfect resources to use. It takes me more time to find all the resources then to make the actual graphic. Here are a few places you can find really good resources at.

Google is pretty much the first place people use, it literally has everything. It's pretty straight forward, just search whatever you're looking for and I assure you, you will most likely find it. For instance, I get most of my character PNGs by searching on google and just PNGs in general. Like I wanted a crown for one of my covers, all you have to search is "Crown PNG". You can go a lot more in detail if you want though. I personally always put Tumblr after my searches because I think it gives me better resources.

This is where I get 98% of my resources from, it takes a lot more searching though it's not as straight forward as Google. This makes my life so much easier because a lot of the resources come in packs and I just bulk download them. I go on these crazy binge downloading sessions. It's harder for mobile users to use because you can't download PSDs (I'm pretty sure) and you can't download resource packs which sucks. I recommend Google for mobile users.

WeHeartIt is basically like Pinterest. It has a lot of really good templates and other resources. I personally don't use this but it is a really good site.

I hope this helps, if you have any questions feel free to ask me. Also, requests for what you want me to post next would be awesome!