Security
Do not leave the spare keys to your accommodation in sight, as thieves may not be able to get in easily (those bars at the windows) but it has been known for them to break the window and get the keys and hey presto!
Fit deadlocks to your doors, burglars may find a difficult way in to your home but they need an easy way out, a Yale type latch lock is absolutely useless for this reason. Climbing out a window with a TV or video is too hard.
If you are going out for the day and you are not sure what time you are going to return, then close the curtains ( the Spanish close their curtains during the day in the summer to keep cool) and leave a light on.
Don't carry all your valuables in one purse/handbag/wallet. If you carry a wallet try and keep it in a pocket that you can button. The inside pocket of your jacket is not good.
Be aware of strangers, usually two or three, that try to sell you something, or crowd you or grab you. The idea is that one or two will distract you while the third robs you...get out of the situation quickly.

If you are renting a holiday property and some turns up to "clean" ask for some identification, because it is a known ruse for burglars. The don`t clean your apartment, they simply clean you out!

                                                                                                                                                                

General

Shopping: Don't be put off if your Spanish is not as good as it should be, butchers, bakers are the scariest because you can't just pick up what you want. No problem use 'pointish' point at what you want and use your fingers to say how many (politely of course)

Milk: The fresh milk here is not good at all, so buy the longlife stuff in litre cartons. The brand Asturiana is as close to the real thing and also comes in, semi and skimmed (desnatada) versions

White rings on furniture: usually caused by hot cups!
Mix equal parts of plain old white toothpaste and baking soda and rub for 5 minutes (sometimes more) and hey presto...gone! Try it on an area you can't see first just to make sure though.

Old plastic bottles, whatever size make great individual cloches for those early spring plants, simply cut the bottom off the bottle and place it over the seedling pushing it into the soil or compost to make it stable.
                                                                                                         
Nights can get very cool in the winter here, so when you have a bath, do not empty the bath until you are completely finished in the bathroom, that big lump of water is actually heating the room!

Kitchen
Get all the juice! blast citrus fruit in the microwave for a few seconds before you hit the juicer helps get all the juice out
Bob Watson

Those plastic things that hold six packs together are a death trap for wild life, make sure you cut them up before discarding them

Fry the best easy over egg: Just as you get to the point when you would try to flip the egg (and usually burst the yolk!) carefully add 1 teaspoon of water and place a plate over the frying pan and in about 15 seconds...the perfect easy over egg!

Tips for sun worshippers
Seriously though, I know a lot of people arrive here to escape from the British summer, and want to hit the beaches so they can return home with the bronzed god/goddess look, but a bit of restraint during the first couple of days will pay dividends later on.
The sun can be so hot here in the summer months that you can burn in just 10 minutes! yes 10 minutes.
If you burn the first day of your holidays, not only will you could you ruin your holiday, your skin will probably not recover in time to get a tan before the flight home. 

So take care, and lash on the high protection factor sunscreen for the first couple of days to give your body a chance to get used to the sun, and even then, you should still use sunscreen and cover up during the hottest part of the day which is from around noon to about 2-3pm. 
Remember that cool breeze just hides how hot the sun is.
                                                                                                                                                                    

Tipping
Tipping is accepted but not compulsory in Spain, usually between 5 and 10% is the accepted amount, but if the meal or service was exceptional then its up to you.
But leaving 50 cents as a tip for a 25E bill is an insult. If something was wrong with the meal or service then you should have said something to the waiter.
                                                                                                                                                                      

Save water! we all know how precious water is so try this:
Fill an old one litre plastic bottle with water and place it inside the toilet cistern and every time you flush the loo you have just saved that amount of water, doesn't sound much does it? But over a year it is a significant amount.
Steve Bosnitt