I love doing these Monthly Planners! I usually end up doing one every year even though I make it so that I can kinda use it from year to year. The plastic covers don't really hold up all that well.
Here is the one I did for 2014. I used a sketch I saw on Pinterest, PPA145, simple but very nice!
The DSP is from Stampin' Up! out of the new Occasions Mini, Retro Fresh.
There are no real instructions for doing this.... All I do is measure the inside of the plastic cover and cut the paper slightly smaller that what is measures. I took the staple out of the calendar and punched holes in the DSP after I scored and folded it. Then I put the staple back in, attaching the DSP to the calendar itself. Then you just decorate as you desire.... but don't put to much embellishment on it! Keep it fairly flat so the plastic lasts a little longer :)