Hi there, welcome to the forum and good luck with your plans

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First off, you'll need to qualify for a visa before you can move to the UK - you can't just move there and then try to figure things out like jobs.
Unfortunately, visas can be very difficult to get. If you are not a UK or EU citizen and don't have any family members (i.e. a spouse) who are UK or EU citizens, then your only options will be a student visa or a work visa.
- Tier 2 Work visas are extremely difficult to get these days, unfortunately. You would need get a job and to be sponsored by a UK company for a visa before you can move. However, unless the job is listed on the skills shortage list for the UK (
http://www.ukba.homeoffice.gov.uk/sitecontent/documents/workingintheuk/shortageoccupationlist.pdf), the company has to prove they could not find anyone in the UK or other 26 EU countries who are capable of doing the job before they can hire you... but there are 500 million people in the EU, and unemployment is high right now.
- There is a Tier 2 Intra-Company Transfer visa, but the requirements to get it are pretty high and it's something that your employer will need to sort out the initial sponsorship paperwork for. For example, though, if you wanted to transfer for more than 12 months, you would need to prove that you will be earning over £40,000 a year in the UK - that's the equivalent of $64,000 per year.
- Your other option would be to study in the UK on a Tier 4 student visa - it would most likely mean doing a masters degree or another bachelors, and it is pretty expensive. Unless you have lots of savings, you'd probably need to take out US loans to cover the cost. As a general figure, Tier 4 visa applicants need to show they have a minimum of about $25,000 available to them either in their bank account of by way of a US loan (for the first year of tuition and living costs) before they can apply for the visa.
One other visa option if you are currently a student in the US is the BUNAC Intern in Britain scheme (
http://www.bunac.org/usa/interninbritain/). However, it would only allow you to live in the UK for a maximum of 6 months before you would have to go back to the US. You would also have to secure an internship in the UK before leaving the US.
For more information about the different visas available:
http://www.ukba.homeoffice.gov.uk/http://www.ukvisas.gov.uk/en/