Many small factors come into play when doing DTube I’ll just run over the basic check list

1. upload from pc if you have one
2. use Firefox or chrome browser
3. login with posting key and not with SteemConnect
4. export your videos in mp4 or wav format keeping bitrate low

Thats the basics but with more information as to which error you get and when there are a few tricks you could try, such as

1. log out clear browser cache restart browser log back in with posting key
2. using an inprivate window for chrome or Firefox
3. try the other browser
4. encode in another file format

Sometimes it just comes down to needing to wait for servers and internet connections to stabilize as I experienced a couple days ago.