Most importantly it's imperative you use photographs of cakes that you have designed and made your self don't be tempted to use photographs you find online if your just starting out and don't have many cakes too show. It's wrong on so many levels firstly you may be breaking a copyright law and secondly it's not a true representation of your work. Your collection will soon grow. On saying that if you find a cake that's outstanding being shared online and want to share it on your social media page please make sure the original designer is firstly ok with their work being shared and ensure the cake decorator is credited for his/her work and supply a link to their social media page I think it's just good manners and networking with other cake decorators can be good to get your name out there.
Get the photographs right and take several shots from all different angles and some close ups of the finer details. It's important to make sure the photographs are not taken on the work table still strewn with your tools icing sugar etc.... ( unless it's a photo tutorial. ). The finished cake should ideally have a nice back drop. You can purchase back drops that are specifically designed for cake photography but these are quite costly. I use wall paper samples ) these store away easily and you can have several pieces that you can choose from to match your cake with the added benefit of them being free.
Try and use some different angles than straight on shots these can make more visually pleasing photographs
And props are great too especially for cupcakes choose props that compliment your cakes the £1 shops are great for picking up little props I picked up these little jugs and designed the cupcakes around it for a gift for my mum for Mother's Day a few years ago.
There are several apps that are great for editing your photos and are free to use I personally love pic collage. It's easy to edit and add text and makes great collages either free style or by using one of the many free templates.
Most people prefer to use their company logo or name as a watermark before posting online their are several free watermark apps I prefer to use the text function on my photo editing app it saves jumping from app to app.
Try and use some
Lastly sometimes you just don't get the perfect shot this is where I crop the hell out of the photos to cut out background mess and try and savage something that's not too sad to post on line. I managed to get a few pics of the cake I made my niece for her baby shower and used pic college to edit them all together.