As you have probably heard a thousand times, the job you find is going to depend on the level of English you speak. That is true, however I would say that it’s going to depend on how brave you are. Based on my own experience and always talking about low/intermediate speaking levels, I would separate the jobs in two groups.
I would call the first group kitchen porter/cleaner. For carry out this kind of job, you will not be asked to speak English, but at the same time, you will not practice it and it will be difficult for you to improve your English. Besides, these jobs can be very tough and the possibility to be exploited by your boss is bigger. Whatever the country you go you will come across people who fancy take advantage, and they could try to cheat you because of you don’t speak English and you are desperate to get whatever the job. They could try to pay you less than the minimum or just take money from your wage.
The second group could be called waitress/shop assistant. I strongly recommend you try to get one of these jobs. As I wrote before, the level of your spoken English is very important but even more important is how brave and keen you show yourself about get the job. I know how much it scares to face a job like this (I am not going to understand them, they are not going to understand me, I am going to make a fool of myself), dude. Show your best smile, try to tune your listening at 200% (but showing lots of confidence in your face) and the job will be yours before you think. Afterwards come the tough two first weeks until you get use to the specific vocabulary related to your job (at the end it is a hundred words repeated thousands of times, just need to endure those two first weeks). In my case, I working in a sports shop, I used to look for the help of my colleages (nice and helpful people, by the way) when I didn’t understand what a customer was asking me (I still do it hahaha) Use sentences like “I am new so if you wait a second I’ll ask to one of my colleages”. If you get one of these jobs, you will be in contact with customers (which will improve a lot your listening and fluency) besides you will work in an atmosphere open to the dialog with the staff, make new friends and to talk a lot, that is what you need after all in order to improve your English.
About wages, in a lot of the shops, restaurant and coffeeshops you will be paid the minimum, wich is not too bad and can be enough for make a living. Nevertheless if you could get a job in Tesco or Sainsbury’s supermarkets, that would be awesome. It seems that they pay very well, in the other hand I have to say that I haven’t come across many Spaniards there. I ignore the reason. Maybe I'm wrong...
A very important factor to keep in mind when it is about getting a job (and about take the decision of when to move here) is the time of the year. For example, for this Christmas restaurants, shops, etc. have been recruiting a lot of people. The reason is easy to imagine, in these days the consume grows a lot thus companies need reinforcing their staff (Christmas jobs, as they call it) On the other hand January and February seem to be bad months for get a job, companies have more excess than lack of staff and find a job can be more difficult.
Other thing very important is the universitary calendar. There are thousands of students living in Bristol, and exam’s time and of course the end of the course (when they come back home for the summer break) are periods where a lot of those students leave their jobs free. Shall we say that may/june can be a good moment for arrive in Bristol and start looking for a job.
The best way to look for a job (apart of find out in Gumtree, Evening Post, etc.) is to buy a map (the A-Z is great and costs 5 pounds) and jump to the streets, spreading the wittiness and hapiness we are known for, and sooner than after you will get a job. The “corridor” Cabot Circus- Harbour- Park Street- Clifton- Whiteladies Road could be a good zone to start from. It would be rare if you need to go further to get a job. If that happens and the time passes without have a positive answer, don’t hesitate in make your geographical horizon bigger and be patient, eventually you will get it.
My arguments are based in my own and my friend’s experiences. I have generalized and summarize a lot but the truth is that with the level of English that the mosto of us have when we arrive in England we can expect to go too far. Of course as your level grows you can try to work in something related with your studies or career, but so far I can’t say too much about that.