a good hotel to stay at is the pathumwan princess, it is linked
to MBK and is very near siam square...
the hotel has a full brekky spread so you can have "brunch" and
then head out... make sure you go over a week end and go to
chatuchak you can get there by taking the trains or maybe by tuk
tuk... my advice is not to use a taxi otherwise they will take you
to all the must stop tourist place to look at "tourist"
products...
also you have to go to siam square to eat the steamboat and to eat
the kobe beef.
don't forget also that the pathumwan princess has a really good
japanese restaurant and a korean restaurant too... if you are
fortunate enough, they will have their buffet promotion where you
can have all you can eat jap and korean food for about $30 sing...
the jap food includes tempura, teppanyaki, sushi etc... if you want
a nice cosy dinner in the room, their room service food is very
good. their buffet spread for dinner and supper is open till 1 am i
think.
the food court at the top of the MBK centre also has very good
food.
chinatown is a must to eat the birds nest, and for the really good
food too... also very very cheap...
late night shopping at pat pong.. but be good ya, no tiger shows...

hope you have your accommodation booked and your transfers
arranged, otherwise, best to take either a taxi or a merc limo from
the airport as they can arrange for two way transfers as well. if
you want to get into the city quick, then pay the extra 70 baht of
thereabouts and take the highway.
At the airport, you can also arrange for free tours of thailand as
part of their tourist promo, but if you are not into buildings and
culture, not so fun.
before I forget, visit the mandrin hotel...
other places to shop are the world trade centre and the other place
for computer stuff... but then walking around MBK can occupy you
for a couple of days.. 
and get your fill of foot massages and massages if you want, the
pathumwan princess are arrange them in your room for you as they
have a full service in house. They also have a very good gym and a
nice swimming pool.