To get to Brighton from London, you can take a train from London Victoria or London Bridge station. The journey takes about an hour and costs around £15-20 depending on the time of day. Once in Brighton, you can walk to most of the attractions in the city center. Alternatively, you can take a bus or taxi if you prefer.
If you have more time, consider visiting the Brighton Pier, the British Airways i360 observation tower or taking a boat tour. For those with less time, skip the Brighton Museum & Art Gallery or the Preston Park. Don't forget to bring comfortable shoes and a jacket, as Brighton can be quite windy.