I've had a variety of jobs in my lifetime, and most of them have given me very little autonomy over my workplace environment. I've worked retail, in a fancy bakery, a couple of video stores* and a slew of offices, with my current gig at four years (and counting) being my longest one yet. Because I've earned my living in such a variety of work environs, I've come to appreciate how fortunate I am to have a little bit of wiggle room when it comes to the decor of the workspace.
First off, I hang on to a general rule about desk accoutrements. A long time ago I came across a piece of advice that said to keep the amount of plastic items on your desk to a minimum. The impetus behind this rationale was to lessen the feeling of working in a cold, artificial environment. Now, some things almost
have to be made of plastic, but I welcome opportunities to incorporate other materials into my work world, like glass, ceramics, wood, metals, paper, and natural vegetation. That gray
Jonanthan Adler head vase was a gift from my friend
Annie. Every Monday morning I buy some cheap fresh flowers and plop them in.
The little ceramic ox was a gift from a coworker for Chinese New Year a few years ago, and the little glass fish bowl is from Venice, a place I went to many years ago. In the background there is an old Valentine's Day card from Ted. The design is a replica of a vintage Valentine wherein a frosting tube is talking to a cake. It's absurdly charming, and makes me smile every time I look at it.
The Dia de los Muertos tableau in the wood and glass box was a gift from a friend traveling through Mexico. The bright blue paint on the sides is very similar to the color of the Rolodex about twelve inches away, which strikes a nice balance and creates an unexpected bright blue color story. The ceramic mug bearing my initial ($6 at Anthropologie) serves as a cup holder for my afternoon iced lattes - I hate the condensation accumulation but am
not about to have a coaster on my desk.
Having a single framed photo on your desk is another more obvious way of lending a personal touch, but it can also serve a dual purpose. Where I currently work I do not have any issues with unwelcome workplace flirtatiousness, but I sure did at some previous jobs. If you are coupled, a framed photo of you and your sweetie sends a strong message. It's much easier than wearing a fake engagement ring (which I will admit to having done in my younger days). I got that black frame for about two dollars at a thrift store. I wanted something basic and professional and this works nicely. I'm not really a fan of going nuts with a million framed photos on your desk because that can look cluttered very quickly.

That pen cup is actually a large drinking glass I got at a thrift store for a dollar. I got tired of looking at the perforated plastic cup that had been passed down to me and took the long-ago heard advice of lessening the plastic. The transparency of the clear glass also lets me find what I'm looking for a lot quicker rather than just relying on what I can see poking out of the top. That large Post It Note holder actually is plastic, but looks like glass. About nine years ago I started working at my first real office job. I had no idea which end was up and really bumbled through my first few weeks there. The office manager, Gayle, was a great mentor to me. She had this exact holder on her desk and I really liked how it looked. Four years ago when I began my current job I learned that the exact same holder was still being made, so I ordered one for myself. It's functional, of course, but also a bit aspirational, a reminder of the kindness she bestowed upon me as I was still getting my water wings.

We'll end with the day planners. That is plural on purpose. My job situation is as such that I don't have to take my work home with me, ever. I figured out a while back that keeping my big boring work day planner for work and my "me" day planner separate was good, uh, planning. So, the work planner is all business, and the Kate Spade one is fun, punchy, and small enough to tote around with me as I live my life outside of the workplace.
* I can't wait to regale my little niece and nephew with stories about what video stores were back in the olden days.