After a month of stubbornly ignoring all the good advice from chess.com forums about the importance of tactics and end game for beginners (and not openings!), I would now like some suggestions as to best way of doing this! 

Priorities:

1. Basic mates with rook, queen, two bishops, knight and bishop, king and pawn against king.
2. Do as many tactic puzzles as you can. Tactics Trainer, google search for other resources (I'm not allowed to post links) or pick up some books full of problems.
   
3. More complicated endgames - basic rook and pawn endgames, learning things like the Lucena position, work through classic endgame studies to see themes of creating weaknesses, triangluation, that kind of thing.
   
4. If you've been doing this for a while and your rating starts to plateau, then it might be time to study one or two openings and work on positional play.

Many thanks to your posting thefox31!