Visual Exercise is Good for You by Rob Sheppard
In this post, Sheppard offers a few ideas for visual exercises to keep your skills sharp & have fun. One suggestion is to photograph the same scene with both a wide angle and a telephoto focal length. Below are two examples.
|Wide angle left; telephoto right|
|Wide angle top; telephoto bottom|
These web sites provide lists of topics and ideas you can explore with your camera.
33 Easy Photography Projects to Strengthen Your Portfolio
My favorite ideas from this site are ones that have you photographing over a time period, making (and sharing) a photo a week (52 annually) or a photo a day (365 annually). Either requires a commitment on your part. If those seem like a daunting project, try a photo a day for a month. That's only 30 pictures, less than a roll of film (from the good ol' days).
15 Creative Photography Project Ideas to Get You Shooting
This site's unique suggestions include "geophoto", photographing locations of geocaches; homelessness, paying homeless people $2 to make their picture; photographing one of your meals a day for a month; and making 10 visits to the same landscape location in a month.
Photography Projects: 21 great ideas for creative photos
From this post, I like "From the Hip," shooting without looking through the camera on your daily commute or weekly stroll; "Project 50," using a 50mm lens for 50 days to create 50 photos (you could pick any focal length/days/photos combination); and "City Swap," photographing in a town completely different from yours.
If you would rather review a book of ideas and examples, check out these options.
Ten Photo Assignments to develop your photographic skills by Amanda Quintenz-Fiedler (available in paperback or electronic version)
This book contains 10 exercises to help you get to know your camera controls better. While it often suggests extra equipment (like a hand-held incident light meter), you don't need these things to complete the exercises.
Photo Idea Index by Jim Krause
This book contains a plethora of ideas for digital photography projects. The author has made all the pictures in the book using both point & shoot as well as DSLR model cameras. And he encourages photo editing techniques to expand your results. Though it appears to be out of print, there are plentiful used copies available for next to nothing.
Taking a look at any of these options should give you plenty of material for a winter of photography exploration and beyond.