Would love to hear your thoughts on how you keep from getting stale and continuing to challenge your creative side. Here's one to get started

Take from outside your immediate genre or style:
If you only have one influence you're unlikely to make anything new. Be taking ideas from as many different things as possible so that you can be inspired to bring something new to those who come to you. This means you must also be ok with sometimes creating things that don't neatly fit into any boxes.

This may also mean going to an art gallery, dance competition or poetry slam. Seeing different forms of expression will not only help you better understand how you express your creativity, but how people will receive your creation. It will give you a new perspective to help articulate your thoughts.
I've been doing that 'write a song ever day for 30 days' challenge-thingy (I'm going for 50). I've been coming up with some cool/different stuff.

I guess I would say, if anything, it's keeping my mind pretty sharp and creative and has helped me realize that you have a lot more inspiring moments and grow much quicker if you keep writing all the damn time.

It might seem difficult for the first 20 minutes, but as long as you know how to play your instrument and have a little know-how when it comes to constructing music, there's no reason why you can't pen a song every day or twice a week or whatever. Songs will always write themselves. You just have to put in the effort.

I mean, don't get it confused. I've written a lot of shit in the past 12 days but I've also come up with about 2-3 good songs and one that I think could be great. Not every effort will turn out to be genius but you can't get to genius without trying first.
I like to experiment with different tunings on my guitar. Typically I'll write in a dropped or standard tuning, but recently I've been trying out some open tunings, like DADGAD, on my acoustic. Another tuning I've been using is BADGBE.