Design

- Be Creative
Obviously. This cannot be taught in any coaching classes or books or whatever, Think out of the box.Think of all the crazy ideas even though they might be silly(humour is also an added advantage sometimes)
- Speed Sketching
Practice speed sketching cause there are a lot of questions and you have less time to think and execute.Practice practice practice, stretch you won't break your wrist while speed draw sketched your limits. Ask your friend to give a random topic and you sketch it as fast as you can.
- Choose drawing overwriting
Although some questions do give you an option to write your answer or illustrate I'd suggest you sketch down your answers as this will have an advantage over written answers.
- Current Affairs
Even though there was only one question (4 sub-questions) last year that tested your GK, you don't want to lose marks on such things so go through all the current affairs for the past one-two years.
- Coloring is an added value
Some questions compulsorily require colours and you can't bypass that but for questions that don't really need any colours, adding them would be an advantage, But I suggest you keep the colouring part for those questions during the last few minutes when you're done answering everything.
Im an engineer and I didn't go for any art or coaching classes so I'm not sure what they'll teach you.3-4 months of practice is enough but it totally depends on your skills, check out NID preparation blogs, NID PG 2015 or CEED 2015 Facebook groups, anthere's alsa NID Alumni site (National Institute Of Design integrated Alumni Network And students) where seniors can help you.

Yes, BA in fashion designing is a good course to pursue.
India which has always been a centre for the textile and garment trade is also growing into a centre of innovation in the garment and accessory design. Fashion technology has a wide scope for choosing a career. Now the fashion industry has become so specialised that it encompasses a vast field of studies in design, concept management, design production management, quality control, planning, fabric design, printing, fashion accessory design, fashion merchandising, textile science, colour mixing, marketing and so on.
The primary areas of work in the fashion industry are market research, designing and manufacturing of garments and textiles.
Fashion Design is the most important area of work in fashion industry. Designing involves creating original designs after studying the changing trends of the market i.e market research. It has various fields of specialisation like garments, footwear, jewellery and even luggage. It is a challenging field as it requires the coordination of various jobs, in small concerns it is usually a one man show but in big organisations, the jobs are specialised and allotted to different people.