Schengen visa to study in Germany refused

Item 2 is pretty self-explanatory, you need more money in your bank account or evidence of salary being paid while you travel. You can pad your account with money from family or friends, but don't just put one big lump sum in, as consular officials are wise to that trick. Add the money in smaller chunks over several weeks.

Item 3 is a sticking point for many visa applications for people from developing or third world countries. They want to see evidence you are motivated to return home. This can include owning a house, children or parents that you support / take care of, a very desireable job that is guaranteed for your return, etc. And unfortunately, these can sometimes be hard to document (except owning your own house).

Tom already provided good advice (+1 to his answer) but I just noticed your comment. You apparently submitted documentation (leave from your work, tuition fees and funds) for a three-month stay while registering to a six-month program that you cannot possibly complete on a short-stay visa. That's a big no-no that would make your application look very suspicious. It must have looked like this language program is just a pretext for you to enter Germany and do something else during these three months or even stay illegally in the country after that.

Beside following Tom's advice, you definitely need to either find a three-month program or apply for the right type of visa (and even that might be difficult in your situation).

I think you should apply for a student visa, not a Schengen visa. Schengen visa is for short stays only, usually with the main purpose of tourism. A different visa applies for those who plan to study in the EU. :)