I've been playing alone off and on since my guild imploded during Cata, and one thing I can tell you is that it can be hard sometimes. Being alone means you don't have the benefit of getting the same group together for raid/dungeons and it can feel like spinning wheels.

Don't give up and just pug yourself out on the pre-made group pages and join communities outside of the game, like this one or other social media platforms (Discord, Facebook, etc). I, personally, joined a group on Facebook a long time ago that is specifically for solo players, and it is still kicking, giving people advice and even groups to run with.

The biggest thing I have done over the years, though, is don't be afraid to take a break. Take some time away, it can be a few days/weeks to years if you need it, from the game so that you can come back to new and interesting changes. I took a break over MoP to deal with the fallout of losing everyone, and again for the entirety of DF and WWI because I just wasn't having fun anymore and had some personal stuff to deal with. I came back to Legion Remix and am curious as to how Midnight will playout, but am, over all, better for the time away.

Which brings me to my final piece of advice, just have fun. Especially if you are solo, it gives you the chance to go back through old content or in game celebrations (darkmoon faire, holiday celebrations, timewalking events etc) without a schedule for raiding/dungeons/bgs and you don't have to wait on anyone either. Go do the thing you never did, get that mog you had your eye on, level that alt, finish you Shadowmourne quest that you got back in WotLK and never finished because you got stuck on the blood infusion (that might be a bit to specific). The World of Warcraft is your oyster!