Russian consulates in some countries or at certain consulates they may ask you to present the original visa support document and not a copy, for example; the Russian consulate in Beijing in China requires an original document while the one at Shanghai does not. If the consulate you want to apply too requires the original then this can be sent to you by courier from Moscow at an additional cost.
It is important that you are aware that the visa will only be issued and valid based on the dates that are recorded in the visa support documents, if you are not sure of your entry or exit dates then it is possible to request the support documents for a few days before and after your expected dates and then travel within this period.
If you are not a national of the country you are applying for your visa in, then Russian visa regulations require that you prove you have been legally resident in the country for at least 90 days before they will issue the visa. If you can not prove your residency then you will need to apply in your home country. Some consulates allow you to apply without the residency requirement being met, though will take a minimum of 10 working days to process the visa.
Applying for your Russian visa in the UK is a relatively straight forward process though please ensure that you check your visa carefully when you receive it and ensure that it is suitable for your travel requirements.
And finally, when you are in Russia, please remember to register your visa.