Please help me in making the perfect itinerary for Hong Kong. Going on a holiday for 4 days there.?

I would plan your itinerary based on the location of the attractions (to save traveling time).

Hong Kong Island (1st day)
- Repulse Bay
- Ocean Park (you might want to spend one full day there)
- Causeway Bay (go there at night)

New Territories and Kowloon (2nd day)
- Tai Fu Tai - Tai-Po
- HK Heritage Museum – Sha Tin
- Wong Tai Sin Temple – Wong Tai Sin
- HK Museum of Art – Tsim Sha Tsui
- HK Museum of History – Tsim Sha Tsui
- Ocean Terminal / Harbor City (shopping mall) – Tsim Sha Tsui
- One Peking Road
- Avenue of Stars, Symphony of Lights, Clock Tower (it's better to watch the lights from the Kowloon side with the Hong Kong Island side as backdrop)
- Ladies Market / Temple Street Night Market (go at night)

Hong Kong Island (3rd day)
- Hong Kong Arts Centre – Wanchai
- Western Market – Central
- Flagstaff House Museum of Tea Ware - Central
- Peak/ Madame Tussauds
- Hollywood Road / Man Mo Temple – Sheung Wan
- Lan Kwai Fong / Soho – Central (go at night)

Lantau Island (4th day)
- Ngong Ping / Ngong Ping Village
- Buddha / Po Lin Monastery
- Disneyland (it's so small you only need a couple hours)

Sorry, I am not that familiar with the Octopus Tourist pass, because every time I go to Hong Kong, I just get the regular Octopus pass.

Places to visit are The Victoria Peak which you can take a tram ride up from behind the large HSBC building in Central. Once up there, take a walk around the rim to get birds eye views of the city. The HK Madame Tussauds is also up there if you're interested. In Central, loads of places to do shopping with unique little boutique shops in around the Soho area which also has the worlds longest covered escalators. Loads of cuisines to choose from aswell there. Take a HK$2 tram ride right across the island to take in the sights. You might want to jump off at Causeway Bay (aka CWB) where it's shopping galore.

There is also Lan Kwai Fong in Central, Hong Kong's hippest nightlife area. This is where it all happens with hundreds of bars which you can find and read reviews on this site which I found useful:

http://www.hongkongbarsclubs.com/clubbing/lan-kwai-fong/

before heading there to save time. Some bars also offer great views of the city such as the Zen Lounge of the Sheraton Hotel http://www.hongkongbarsclubs.com/tsim-sha-tsui/zen-lounge.html but that's across in Tsim Sha Tsui (aka TST) which you can take a HK$1.8 cheap Star ferry ride across the harbour. Once over there, again it's shopping paradise and also has a few museums:

http://www.discoverhongkong.com/eng/attractions/museum.html

for a full list. walk along the harbour at TST which will take you through Avenue of Stars and give you great views of the city esp. at night. You should also check out the Symphony of Lights daily where you are treated to a spectacular light show with music for free.

Other places to visit are Ngong Ping 360, the cable cars from Tung Chung (outlet centre) which takes you up to the Big Buddha and again there's a souvenirs shopping street there. Ocean Park which is a great theme park with live animal shows, rides and a good day out. DisneyLand which is quite small but worth the visit.

Don't neglect the New Territories area (aka NT) because this is where you see the local side of the city, the real HK. Areas to stop off on the train in NT are Shatin, and Tai Po.

the 3-day tourist pass might be limited to just the MTR, and not all lines at that. since you will most likely take the bus (to stanley), the tram, and the ferry, i suggest just getting an on-loan pass then refund it before you leave hong kong.

other places you might want to see:
at New Territories/ Diamond hill:
http://www.trifter.com/Asia-&-Pacific/Hong-Kong/Reliving-Tradition-at-Nan-Lian-Garden-Hong-Kong.729619

a coffee shop at TST:
http://www.trifter.com/Asia-&-Pacific/Hong-Kong/A-Cup-of-Joe-Served-by-Chuck.748193

a little something about commuting around HK:
http://www.trifter.com/Asia-&-Pacific/Hong-Kong/Getting-Around-Hong-Kong.751399

Street markets: the prices at stanley are very high compared to Mong Kok and Prince Edward. My favorite street market is Prince Edward --prices are a bit cheaper, and Temple Street.