Which terminal at Heathrow?
terminal 2 if you're flying from Prague with Czech airlines, or terminal
5 if you're flying with British Airways.
(for more info : http://www.heathrowairport.com/portal/
page/Heathrow^General^Flight+information^Which+terminal?/)
Terminal 2 & 5 have the same route, but if you're flying into another
terminal please check, quickest way is to take heathrow express to London
Paddington, then take the underground (bakerloo line) to charing cross
(direction: towards elephant and castle)
The express is very expensive however.. about £15!!
If you wish to travel cheaper you can take the „heathrow connect“ which is
£6.90 to London Paddington.
All the travel planners will suggest you use the Express as it's faster, but
its so much more expensive, so I doubt you'll find it's worth it..
for this info I used: http://journeyplanner.tfl.gov.uk
From Charing Cross there is a train direct to Hastings.
Hope this helps, and that you understand it all!
Cheers
Andrew