There is actually no some hard and fast trend regarding what to do before mba you can opt for engineering,commerce or arts even courses like CA and CS can prove helpful ,basically MBA as a course requires analytical thinking and it can be  pursued after any stream but yes engineer have a distinct advantage in entrance exams due to there mathematical background but other streams can also be on par with engineers depending on there hard work.

Getting B.tech degree then mba is in demand and it has a greater value but if you aren't intersted in engineering then b.com or BBA or bms can be good options.