Let the freezer be your friend
Many people don't realise that cakes freezer really well. If you avoid icing or buttercream you can start to get organized weeks in advance. Always allow your cakes to cool completely and then wrap in a double layer of cling film or freezer wrap. Don't forget to label your cakes as once frozen one cake can look very much like another!
If I need to bake a lot of cakes I tend to fill my freezer first with meals for the next couple of weeks. Once I take out one meal I know I have space for some cakes. Time not spent making meals can be used to bake cakes instead. A freezer is also most efficient when full.
Just because you have never had food poisoning from anything you have cooked doesn't mean you aren't going to make other people sick. You are used to your own cooking but others may not be. Be scrupulous in your cleaning and food storage. Every so often there is a story in a newspaper where a school has banned homemade cakes for their fair for fear of food poisoning. Don't give them ammunition!
If you are baking for an artisan market or trendy farmers' market then go for the chilli chocolate brownies or the ginger and cardamom macarons. However most of the time people will be wanting something that they are familiar with so go for things like lemon drizzle, coffee cakes and never forget anything with chocolate! If you want try something unusual put out a sample plate for people to try.
Costings and pricing
There is no point in baking something which the ingredients have cost you £2.50 if you think the maximum you can sell it for is £2.00. There are plenty of cheap ingredients you can use that don't mean low quality bakes. After Christmas each year the supermarkets reduce mincemeat. I bought jars and jars for 10p each earlier in the year and they are dated until September 2015. Think of the mark-up on your mince pies and fruit cakes!
If you are selling at school fairs always make sure you have plenty of individual items for the children to buy. Many of the kids will rush up to your stall clutching a 10p or 20p piece. Don't disappoint them!
If you are needing to make a lot of cakes set out a plan to use your time most efficiently. Instead of making one 2lb loaf cake make two 1lb cakes instead. Not only will you fill your stall more quickly but you will be able more money from selling two cakes than one large one. Find recipes for cakes that don't take too long to bake. Traybakes can be easily cut up to fill a basket or platter. Double up on fairy cake or cupcake mixtures so while one is baking you can prepare the next batch in the tray.
If a cake doesn't look good it isn't going to sell no matter how good you know it tastes. Make sure the customers can clearly see your cakes so don't wrap them in foil or opaque bags. A little bit of ribbon or coloured string on a cellophane bag can really make a difference. If you are baking for a themed event get a few items like cupcake cases, napkins or tea towels to display your cakes with on. And finally...always remember if a cake looks terrible a drizzle of icing or melted chocolate always does the trick!