language help: A bit of Spanish help. - Help.com

It should be this:

Generalmente, mis fines de semana no son importantes.
(Generally, my weekends are not important)

Or you could also put it like this:

Mis fines de semana, en general, no son de gran importancia.
(My weekends, on general, aren’t of great importance)

again, you can use both variations.

Generalmente, mis fines de semana no eran importantes.
(Generally, my weekends were not important)

Or

Mis fines de semana, en general, no eran de gran importancia.
(My weekends, on general, weren’t of great importance)

So the correct conjugated verb you were looking for was: eran (were) of the verb ser (to be).