Citrus (lemons, limes, mandarins, grapefruit, oranges etc.) like hot, sunny conditions, although you can buy cool climate varieties. They do not respond well to frosts.
Citrus trees are bought grafted and bare rooted. You can buy full size or dwarf varieties. Citrus can be grown in a pot, or in the ground, and can be espaliered. You need to prepare the soil well by digging in plenty of compost, manure and adding in a bit of Dynamic Lifter.
Citrus trees don’t share well; so don’t plant under the canopy area of the tree (this includes grasses), and leave plenty of room between plants. Cover the area with mulch or leaf litter to prevent unwanted growth (of other plants). Don’t place mulch right up to the trunk though, as it may cause rot.
Plant in full sun, water well and fertilise in Spring and Summer. You may use a citrus fertiliser, a seaweed-based fertiliser, and/or dynamic lifter and manure (or all of the above).
Older leaves that yellow in the centre may be an indication of magnesium deficiency. Treat the soil around the tree with Epsom salts (magnesium sulphate). Leaves that yellow at their tips can indicate a lack of fertiliser (use a complete fertiliser).
You may find odd looking lumps/growths on the woody parts of your lemon tree. These are caused by Gall wasps. The only solution (that I know of) is to remove these by cutting off the offending branches. Do not dispose of these in your compost.