My site is offering tax services in uk. Should I promote it in uk or another country?
I think that if your business site (website I presume) is offering any type of tax services for the UK, in the UK, then certainly youe primary clientele would also be in the UK.
Generally, tax laws, ruls and regulations vary a lot in different countries and it might not be wise or advisable, being a UK-based tax services company, for you to try to offer services in other places where these might or might not be relevant.
However, it would still be advisable to a limited extent, to also advertise yourself and your site/company services abroad, in some parts, where (a) large numbers of UK expatriates might be dwellng and working and/or (b) local people might have or be interested in having investments in the UK on which they are liable to pay taxes.
I believe that, under such circumstances, whilst you focus mostly on promoting your business in the UK it would be good to also advertise your services in (say) places like the Middle East (Dubai/UAE, Qatar, Saudi Arabia etc), South Asia (India, Pakistan, Bangladesh), and the far East (Hong Kong, Singapore, Australia/New Zealand, Malaysia and so on) which could prove to be a beneficial step. Good luck.