When keywords are on the top of the google search engine then what to do ?

[JohnDooley]

My two keywords are on the top of my desired market place that means google.co.uk . So now what should I do to sustain this position???

[matbennett]

I'd start thinking about more keywords to target to be honest.  It's really risky to be that narrowly focused and you'll bring in more business by broadening your focus anyway.  As a bonus, work that you do to introduce new target phrases should also strengthen your hold on your primary terms by attracting more authorative links.

[irvingw]

update content, keep it fresh

research keywords more and look to rank for mid tail and long tail

if you have something sellable to the US try to do the same in google.com - much bigger market

don't buy links, make sure the ones you have are sticking around

check your website for errors and performance issues and optimization opportunities always

[SEODinosaur]

Mat and Irving are correct and you can also work on Conversion Rate Optimization. Traffic is one thing, are you generating money? Are the visitors converting into sales? What can you improve to gain results?

[EGOL]

My two keywords are on the top of my desired market place that means google.co.uk . So now what should I do to sustain this position???

Nice work!    The first thing that you should do is praise God!

After that, get right to work on more content for different keywords.  If it starts ranking you will be riding the gravy train.