Hi Minni80,
If you are looking for work in summer, then the best place is unfortunately the Med coast. I say unfortunately as you will be serving Brits, Germans and Swedes, and will not progress far in your Spanish.
As for Madrid, if you go to outlying towns around Madrid (for example Pozuelo, Somosaguas) you can see flyers attached to lampposts etc. Often these are S.American women offering their services as cleaners, nannies etc. I think if you were to offer your services as an English-speaking nanny, you may get a taker(s). Summer however may not be the best time to do this (especially in August as all reasonably wealthy families will re-locate to the beach or the hills for the month). Make sure to have a Spanish mobile/Simm to advertise like this. Also, try looking in
segundamano or even advertising here?
One last suggestion - try the Irish bars (but make sure you have already learnt some Spanish). July may actually be a good time to try if some English teachers who work some nights there head back home.
good luck!!