As a beginner, a steady wind and flat water is what you want. Ideal wind strength is between 10 and 15 knots.
At the coast the ideal is usually a cross shore wind, as it allows you to sail out and back to the same spot, but even if you do go downwind which is inevitable while learning you will still come back into shore and be able to walk back to where you started.
An onshore wind means that you will be blown back on to the beach. It is very challenging to kitesurf in unless you are very competent at getting upwind. Not only this but it usually brings shore break and waves making it even harder to get out. Plus you must bear in mind that if you have any problems (wind picking up or wipeouts etc.) it will involve ending up with a hard landing on the beach or worse still a rock/groin or building!!!
An offshore wind is bad news as a dropping wind, loss of board, equipment breakage could mean a slow trip to France!
If you are planning a trip to the coast, remember to check the tide. A lot of beaches in Britain require a long walk to the waters edge at low tide and some are unsailable at high tide due to sea walls or man made groins. Tidal movements can also mean strong dangerous currents so always get local knowledge when you head to a spot you don’t know!
You will find that conditions in the UK are often not what the weather man promised. Don’t go out if you are not sure! Try another day.