This site is a mine of information on moving to Spain and gives the pluses and minuses of doing so.
Have a look through things like Moving to Spain, What's the area Like, Working in Spain, Living in Spain, Healthcare in Spain etc. There are many good pointers there.
First you need to decide where to go, Spain is a very big and very mixed country. You might want to decide if you prefer the coast or inland for starters.
Then look at the finances. Housing is no longer cheap in Spain with inferior property selling at UK prices. The cost of living is still cheaper than UK but rising rapidly, especially with the shrinking pound. Healthcare can be expensive, and so is social security. Jobs are difficult to come by and pay a lot less than UK. If you can't speak Spanish you will find it very difficult to get any work worth having. Waitressing and bar work are very seasonal and you would rely on tips as the pay for this type of work is only about 3 pound an hour. The first year will be the hardest and you need to ensure you have enough behind you to cover yourself for that year, living expenses, food, entertainment, rent/mortgage etc
Whatever you decide, check out the place and opportunities available thoroughly. Read the posts on this site (and others like it) and then come back and ask as many questions as you like. We are quite a friendly bunch and there are plenty of people willing to help you out but they won't (generally) steer you in the wrong direction by making out it's an easy decision.
Best of Luck with whatever you decide.