"start at half their offer and then build up to aroung 75% percent of their original offer or sometimes even less and don't be affraid to walk off"
start off at 20% and work up to 30%, walk away and they'll give you a deal if it's worth it to them; then again if you're only talking £5 why not give it to them, you'll never buy things as cheap in this country.
Be careful of the currents off some beaches as they can be very strong.
If you want to go somewhere hire a taxi. Get the same bloke every time, he'll appreciate it. It's dirt cheap (cheaper than the organised days out), the driver will show you whats worth seeing and if you go to a beach or something he'll wait all day and then take you home when you're ready - you pay for the waiting time but it's not much and they're great guides and help keep all the beggars at bay etc.
There are some great deserted beaches half an hour from the main areas. We went to one where there was a bar, 4 tourists and a load of fishermen. At about 4pm a coach arrived and it got busy but they were bussed back out an hour later. Beautiful day!