Polytechnic

You should try to understand the fundamentals of your subjects and learn them well.

Somesh, yes you can do it subject to fulfillment of eligibility criteria. You have to appear for Lateral Entry Engineering Test (LEET) for admission to BE/ B.Tech lateral. You must have min.of 60% marks in diploma to appear for LEET.
If you have not given LEET too, then opt for good private universities where you can get admission on basis of your marks in diploma or tests conducted by those universities. Most of these universities offer world class environment to students along with good placements. Some even offer good scholarships to students.
Check their websites. 
Good luck.

Yes . Refer the undermentioned link to understand more about NIOS.
Government Circular for NIOS: The National Institute of Open Schooling (NIOS) http://nios.ac.in/departmentsunits/administration/government-circular-for-nios.aspx --

Romil, check the link below
http://sbmp.ac.in/Fee Structure/M_50
There are some institutions that offer good scholarships to diploma students. they also offer good placements to them.
Also check their websites.
Best of luck.

Hello saurav
Yes polytechnic is a good option after 10 the if you don't want to appear in 11th 12th.but do remember one thing through polytechnic you can only go for B.Tech in future but if you do 12th lots of more option are there which you can choose.
now its up to you and your choice.
All The Best