I’m right there with you! I’ve had mine for a couple of months, and I definitely go through emotional rollercoasters of excitement when I am able to do something, and downtrodden when I feel I have no ideas. I’m starting to pick it back up again. What did I do?
First tutorial I did to make something cool was right off this forum. I battled my way through the voronoi pencil holder, and when it was done was so happy and impressed with the results. Voronoi pencil holder in Inkscape
Then came a lull, but then I thought, let’s make some coasters. I saw the coaster design in the shop, but the problem with it is that I can’t customize it because I couldn’t get the files, so I attempted to recreate it. I really had to go do some lessons on Inkscape in order to be able to create the holder for the coasters. Eventually, I nailed it and was so excited! I quickly ran and cut it out and assembled it, only to realize how difficult it was to glue 3-4 layers of semicircles together accurately that I ended up scrapping it. That is a good lesson, not everything will turn out the way you want, and that’s okay. I had a win by being able to design it, and then just tossed it once I realized I didn’t like the outcome.
I started making more coasters, and then bought some acrylic paints to paint the engraved parts. After I had painted a few I decided I wanted a color chart, so I quickly mocked up a rectangle piece of wood with the words for each of the colors engraved out, and then painted the words to match the colors, so now I have a nifty color chart and I know which ones work well and which ones don’t.
Another thing I did is start asking friends what they would like to see. This got me all sorts of design ideas that I could go tinker with and try and create. When I succeed at one, I give them the piece and it’s great to see how happy and appreciative they are. We both win 
Lastly, I spend a lot of time reading community posts here and on Glowforge related facebook groups. This helps get the creative juices going for sure!
For Inkscape training, I have access to Lynda.com through work, and there is a pretty good class on there, but if you don’t have access to that or don’t want to pay for it, just keep searching youtube videos.
As people have said, its best to just pick something you want to make, even if you are replicating someone else’s work, it is a good learning tool. Then you use pinpointed searches to try and discover/learn how to do the things you need in the tools to get a particular piece of it done. Gives you real world experience and more likely to stick that way
Good luck! Don’t be discouraged! Many of us have NO skill in this stuff what-so-ever. Persevere.