As others have said, you can get tickets in advance, which is advisable in the summer. I went on a July weekday afternoon without a ticket, but waited in line for a few minutes and was able to easily get into the English tour at 2pm. Your hotel concierge can also help you get tickets if that is an easier option.
The tour lasts about 45 minutes and is focused on the family and the history of the monarchy. I was a bit more interested in the furnishings and architecture, but the tour guide didn't really focus on that. It was okay though, as I just spent a few minutes afterwards with the guide, who could answer most of the questions in those areas.
As others have said, there is a lot of construction both on the grounds and inside the palace. It's still enjoyable though.
A lot of folks seemed to be really excited for the 1:30 pm changing of the guard, but I wouldn't recommend scheduling your time around this. It's pretty basic, and anyone who has seen the changing of the guards at most other European palaces would likely be disappointed. It's possible the construction has altered their regular routine.