As your writing part differs between GT And Academic, if it is General then the task is letter writing and if it is academic then iterpretation task .however, the second task is same for both the modules that is generic essay. Your writing part Will be assesed on scoring criteria (4) they are 

Task response/ task achievement

Coherence/cohesion

Lexical resource 

Grammatical range and accuracy 

To get a high score band in writing one must use good vocabulary with linking words , these two will give you high score band

I am not quite sure if you are referring to IELTS Academic or General but irrespective of that, writing task is one tough nut to crack if not approached in the required format. Few things which I would suggest you to follow specially with respect to the essay question which is common to both Academic and General are: stick to the word limit, don't forget to paraprahse the topic followed by your points for and against; besides these practice writing as much as you can and get them assesed by some experienced mentor. These are just a couple of tips beyond which I cannot help in this post but yes definitely these will prove instrumental in setting the tone for your success. Let me know if you need further assistance.

Hi Pavan.

In IELTS writing, not only your grammar and vocabulary should be accurate and versatile, but also you should be able to put your ideas across in a well constructed way. the clarity and flow of idea matters. Also your analytical skills for analysis of graphs should be honed up.

if in jammu, contact vidya learing centre, gandhinagar for help.