I live in Central London - 5mins walk from Marble Arch and can recommend places to eat but it depends on what you like - smart, romantic, busy & lively etc.
Will you be alone or with other people?
Brown's restaurant on St Martins Lane, near Leicester Square tube - close to Covent Gaden , Trafalgar Square & Theatre district is good fun. Browns is very busy & very buzzy. They have a website
http://www.browns-restaurants.com/location_pg/ loc_cov.html where you can do a virtual tour & see menu etc.
If it is your type of thing you could go to National Gallery or National Portrait Gallery in Trafalgar Square, then walk up St. Martins Lane to Browns to eat. Then later if you stroll through Leicester Square and on through Picadilly to Regent street you can see all of that & then catch the bus on Regent Street back to Marble Arch.
If you want to tell me what you like to do I can suggest other things.