If you won't be moving until the end of December, then you can't actually apply for your visa until the end of September - the visa can only be post-dated up to 3 months in advance of the date you wish to travel.
The visa application process doesn't actually take very long, especially not compared to the US visa process (UK visa = a few days/weeks, US visa = 6-8 months), and to be honest, there's not all that much that you can do just yet to prepare for it.
The main thing to concentrate on is collecting the supporting documents that you will need for the visa, but as they need to be dated close to the application date, there isn't much you will be able to collect just yet. You can have a look on the UK visa, Worldbridge and Transpondia websites for information about how to apply and what documents you need to include:
http://www.ukvisas.gov.uk/en/howtoapply/infs/settlementguide, https://www.visainfoservices.com/Pages/Welcome.aspx and
http://londonelegance.com/transpondia/spouse/.As others have mentioned, if you have been married and living together outside the US for more than 4 years, you can qualify for permanent residence right away (instead of having to live in the UK for 2 years first) - however, in order to get it, you need to have taken the Knowledge of Life in the UK test (KOL test), which can only be taken in the UK. If you can take a trip to the UK before you apply for the visa and pass the test while you are there, then when you return to the US you can apply for ILE (indefinite leave to enter) and will have permanent residence right away. If you can't take the test in the UK before you apply, then you can request a spousal visa with KOL Req'd stamp, which means that you can apply for permanent residence in the UK (ILR - indefinite leave to remain) as soon as you have passed the test.
The basic application process/timeline involves:
- Collecting all your supporting documents (bank statements, evidence of employment in the UK or enough savings to support yourselves in the UK, evidence of suitable accommodation in the UK, a sponsor letter from your husband etc.)
- Applying online on the UK visa website, submitting and paying for the visa and making an appointment to have your biometrics taken (fingerprints and photo)
- Attending your biometrics appointment at one of the 129 USCIS application support centers across the US - there are 3 centers in Arizona: Tuscon, Phoenix and Yuma (it can be anywhere from a couple of days to a week or two after you have applied online, depending on appointment availability)
- After your biometrics appointment you need to mail your printed application, stamped biometrics appointment sheet and all your supporting documents to the New York consulate for processing (it must arrive within 14 calendar days of the biometrics appointment).
If you want to have the application processed quickly, you can pay for the priority processing service (it's available on the Worldbridge website) for $300 and the visa should be processed within 15 working days - this can only be purchased on the day you mail your documents to the consulate.
