[@Skwint]

There are some recommendations made inntue rulebook for each class. They actually aren't bad.

Taking fellowship increases for example, always a good idea for the sergeant. It will help you buy other fellowship related abilities down the road. 

And depending if you plan to play your guy as more shooty or stabby, take weapon or ballistic skill increases. These are good places to start.

Or buy a comrade advance. Sergeants have some good ones to pick from.