The emergency exit rows and bassinet positions cannot be pre-assigned. However there are some good (IMHO) seats that can be pre-assigned. Upperdeck bulkhead (row 11) can be pre-assigned since it's neither exit nor bassinet position. If you can get 11A or 11K then do it. Don't get the aisle seat due to proximity to lavatory.

Another good seat to try is 23EF. No window but tons of legroom. 22AB sometimes is disturbed by F/A activities.