what i should do after completing my graduation,is it better to do b.l(hons)as i wanted to prepare for i.a.s?

If its your choice than do it and dont think much about it insteed of thinking of more concentrate on what you want to do, best of luck for IAS.

obtain the syllabus for the same and start preparing for the same. You need to go through 3 stages of rigorous recruitment process called A) Preliminary (consists of two objective papers- i) Optional you can choose and ii) Compulsory ie General studies)(B) Mains consisting of Two optionals; General

If you can go for LL.B., it will be a better option from the point of view of appearing for IAS.