How can f d s come after each other in f-block elements

For a given shell, the energy are determined by (n+l) rule
where n=principle quantum number
and, l=azimuthal quantum number
lower the value of (n+l), lower is the energy of that orbital and hence electron should be first occupied by these lower energy orbitals.
For same number of n+l value, it is assumed that lower n value i orbital should be occupied first.
so for a given shell, the order is s<p<d<f