I think first and foremost, new users need to be made aware that there is such a thing as bandwidth at all. Currently, without any 3rd party site or tool, it is just not clear to see how much you have left. 
Maybe a tooltip or popover screen showing bandwidth left every time you post or comment could help. 

I don’t think having them pay for more bandwidth is the way to go although they have that option available by investing and powering up Steem. Afterall, the beauty of Steemit is that it allows to roll into crypto without initial investment. For me, thats a real strong selling point. 

I’m not sure what the right solution would be, but awareness is certainly key in my opinion.