What always works is to concentrate on blocks which cannot be obtained by farms and/or crafting. For example: coal blocks are always decently in demand. They're kind of special (pitch black) and you won't be able to easily obtain them other than mining. Same can be said about the ore blocks (coal, iron, redstone, gold, lapis, emerald and diamond ore blocks) though you'll need a silk pick for those. Also: /vote. The more (longer) you vote the higher the rewards. The trick is to vote daily which will give you re-occurring awards and one time only awards (like the voter tools). Just for context: I just voted on 2 sites and got 700 + 150 rupees for that. Chances are also high that I'll find something in my /mail (usually a variety of diamonds and emeralds).
make ur own shop! or if u have probs getting started try asking a big mall if u can use some of their chests 2 sell ur stuff. some will allow 4 that b/c more shop signs means more ppl visiting 2 try and get good deals.
If you have any minecraft "talent" Like building fancy things or making really good redstone contraptions with the EMC mechhanics and rules, the best way to make a lot of ruppees is making that into a service. My buildservice went such good that I had to put some projects on hold, just becuase I have way to many to do. (even with only doing things in creative/singleplayer) So that works fine. Next to that, indeed, voting, quartz, shulkers, obsidian, leather and crafting dispensers (Tom and I made 100Kr with crafting a DC of them... It took us some time though...) A blaze and Wither skeleton farm are, if you're good at redstone, also a great idea. Blaze rods, coal and wither skeleton heads are qiute high on demand.
Find something which the market wants and sell lots of it, make it cheaper than the market value to get more sales then you get more money.
