It's more what to avoid than what to include when you have a dairy-free guest (I have a good friend who is dairy free). There's the obvious stuff like milk, cream, cheese butter but also check anything you haven't made from scratch (pastry might contain dairy and shop-bought bread and cooked meats sometimes do too). My friend used to be able to eat Green & Blacks dark choc but it is now made in the same factory as milk choc and the tiny amount of cross contamination triggers her symptoms.
So, some ideas, larged based on my friends tastes. Salads with lots of veg (roasted root veg is great with couscous and a bit of harissa paste at this time of year), some nice meat or fish, etc. If your guest is only lactose intolerant but can eat eggs then mayonnaise based dressings should be fine too. East and South asian cuisines (Indian, Chinese, Thai, Japanese etc) are largely dairy free so take some inspiration from there. Basically, think about what you are cooking and try to give yourself minimal extra work. You may find a lot of your planned dishes will suit your guest with a few small changes (for example using oil instead of butter on meat). For any baking, Vitalite is the best dairy-free spread (the soya ones make your cakes go all funny!)
Sorry, I rambled on a bit there - but hope its given you some ideas