Firstly you need a notebook. Most notebooks will do the job, but make sure the paper is thick enough that whatever pens you are using don't bleed through. I would avoid glue bound books in favour of stitch or spiral bound as the pages can fall out a glue bound book after a lot of use (as I discovered part way in to my year's journal!)
Next is pens, any pen you like! Gel pens are good for not bleeding through pages and come in some great colours but my favourite basic is the Uni-pin fine liner that comes in a variety of thicknesses. And I do love to use a classic fountain pen too.
Photos are a great addition to a journal, there's nothing like a photo to make memories come flooding back! Instant cameras are great for journaling as you go. I have a Fujifilm Instax mini 8 which I love. The film isn't cheap but it's perfect if you want an instant photo in your journal. Printing off photos is important too in this day and age of the digital world. Whether it be with a home printer or online there are lots of ways to get it done and it is worth it for the memories!
My favourite glue for sticking in photos or other memorabilia (Ticket stubbs, labels, tags, lost and found items, anything goes!) is by far Pritt Stick. I also use double sided sticky tape but avoid liquid glues as these can wrinkle your pages.
Stickers are an instant way to add fun and colour to your journal, I always keep a big stock lying around to fill in any gaps and make my journal look pretty.
If you're not in a writing mood but want to include something that sums up how you're feeling adding a quote can be perfect. It's amazing how someone you've never met can put your thoughts so perfectly in to words. You can find a never ending supply on Pinterest and there a lots of lovely books filled with quotes out there too,
Finally little works of art, you might think you're the kind of person who can't draw but there are always ways to add your creative touch to your journal. Even if it's a little doodle of your coffee cup or something in your day you will be surprised at how quickly you improve, as they say 'practice makes pefect!' If doodling/drawing is not your thing, try some stamps and ink or a splash of paint. Washi tape is the easiest and quickest way to add colour to your journal and there is pretty much every pattern you could ever wish for out there (beware though, it is strangely addictive!!)
I hope you enjoyed this and happy journaling! I'm thinking of compiling some of my journal pages for a blog post so if you'd be interested in that let me know!