For these kinds of cases, I think, for each term, multiplication of the summation of the missing term and it's complement works well.
for instance in this particular example,
f(x,y,z)=x'z+yz+yz'
=x'z.(y+y')+yz.(x+x')+yz'.(x+x')
=x'yz+x'y'z+xyz+x'yz+xyz'+x'yz'
=x'y'z+x'yz'+x'yz+xyz'+xyz
Hope this helps.