Who, What, When, Where, Why and How. That's always the best and easiest place to start. You don't have to try and answer all of them, but the who, what, when and where are the most important. They tell most of the story. Then you can think about the feelings you had when the picure was taken (if you were present) and how the subject(s) were feeling or you perceived they felt.
Use your own handwriting. Save computer fonts for titles and borders. It's okay to do a little handmade creative lettering, but let your handwriting tell the main story. It's an expression of yourself, and will be more appreciated. (Okay, maybe there is an exception if you truly have ineligible handwriting, but try!)
You can "border" pictures with journaling, or use die-duts. Use colors and shapes that match the layout.
Don't limit yourself to writing in straight lines. Try making it wavy, using a border template, or trace a shape lightly (erase the lines after) and fill it in with journaling so the words take on the shape.
Keep a small calendar (or notebook, but make sure you write the date!) with your camera so you can record things you want to remember about the pictures to include in your journaling.
If you want to avoid mistakes, write lightly in pencil first and proofread or write on a piece of coordinating cardstock before you adhere it to the page (that way if you make a mistake, you can turn it over or throw it in the scrap pile).
Have others who were present at the events pictured to add their own journaling with their name at the end.
Make a timeline of events. This is especially wonderful for baby's firsts.