Tactics - Long and Hard or Short and Easy?

I want to concentrate solely on chess tactics over the next couple of months. Do you think it is more productive to do harder puzzles, whereby you are spending 10-15 minutes per puzzle or lots of shorter puzzles, where it might take you a few minutes per puzzle or so. (Or a combination of both?)

Thanks.

Any suggestions? Ta.

If you want to focus on tactics, then your general goal is to learn new patterns.  So you don't want puzzles you can solve 100% correct within a few minutes.

On the other side you woudln't want a puzzle where you spend 10-15 minutes and are still honestly unsure what the first move is.

So make them hard, but not completely baffling :)  The point is to see the idea, maybe the first move or two, but you can't quite see it to the end or make the sequence work.  Then when you fail, you look up the answer.  Before the end of your tactic session, you go over all the solutions you didn't get, to in effect memorize those patterns.  You can even begin the next session by first seeing if you can solve the puzzles you missed from the previous day.  If you can't, then go over the solutions again.

I've mostly solved from books where it's easy for me to mark puzzles I've failed each time I've failed them.  From time to time I still pick one of those books up and only attempt the ones with a few fail marks on them heh.

Thanks a lot Wafflemaster. That makes a great deal of sense. I especially like the idea of looking over the previous days puzzles to help cement the ideas. I've been using tactics trainer for a long time, probably too long, but it is a bit, click, click, click, so I have begun to return to the books to look a little more deeply and slowly. I've never thought to look over the previously days puzzles though, I can't believe I haven't thought of that. Thanks again, I appreciate the reply.