SSRS and parameter optional

Hi

I have 4 parameters that should be optional - specified by the client. Thus can choose parameter 1 or not, parameter 2 or not etc.

How will I code this in a SP?

e.g.

Select mycolumn1, mycolumn2, mycolumn3, mycolumn4

from mytable

where (case when mycolumn1 <> 'none' then mycolumn1 = @myparam1 end) --this obviously gives an error

Please help

Thanks