I know, everyone's wretched band director had them bring their instrument home everyday, not practice, then convince their parents to lie at the end of the week and sign this arbitrary sheet called a 'practice log' saying you had practiced an hour a day. This is truly unfortunate because this is the exact opposite of what a practice log should be. A practice log is an objective recounting of how much time you spent doing what in your practice time: no more, no less. Some people get really fancy with them, writing down detail after detail. That's not what I'm doing here. Above is a very simple practice log that I thought would be helpful for anyone looking to improve their practice routine, either by practicing more efficient, or by keeping better track of their own progress, or both. While you don't want the log to go on for pages, it is helpful to keep small notes as you progress (e.g. faster tempo markings, new exercises, etc.). Write down the individual times per exercise or concept and then add them up at the end to see how much you practiced in a day. It's pretty self explanatory, but I'll take you through it. The first field listed is "Instrument", that's mainly for anyone who is a multi-instrumentalist and is juggling multiple practice schedules, in which case, a practice log is almost necessary to track of everything. The next is the date for the beginning of that week. Below that field are the goals for that week. This will help you keep track of your progress from week to week. You write down what you and your teacher have decided you'll work on for the week. The table is a breakdown of time spent on each category and total time per day. That's it.
This table is simple on purpose. You want to spend as little time as possible 'book-keeping' and as much time as you can practicing. Remember, this is for you, not for someone else (so no need to lie). It's a way for you to objectively evaluate where you're at, how to set goals, how to proceed with your practice routine, and the results of those efforts.
I've included a link to Word document so that people can open it on their machine and edit it as need be: