you have to be firm but sympathetic,my son went through this stage and it is hard.
when he used to cry for the silliest things i just sat him down and talked to him to find out what and why he was crying,sometimes when its something silly i would tell him that this isnt the way to get my attention and that he would just end up being sat on the stairs or in his room untill he stopped.
slowly but surely he realised that he wasnt getting my attention,because most of the time thats all he wanted.
try having a word with your health visitor they may be able to give you more advise or leaflets to help with the problem,good luck and i hope this helps ;0)
keep smiling.