It depends on which kind of points you're chasing. If it's good old first-geograph points you're after, the answer is probably 'Ireland', although a handful are still left on the big island too. Many of them are mudflats and military installations, though, so good planning and potentially letter writing for permission may be involved. First-geograph points are available in squares shown in green or orange on this map http://www.geograph.org.uk/mapbrowse.php - zoom into your region of interest. Occasionally, squares that have become 'green' again because a mislocated photo was moved are announced on the forum at http://www.geograph.org.uk/discuss/index.php?&action=vthread&forum=2&topic=8428&page=0 . Expect an imminent mass pilgrimage of Geograph-ers to these, though!
There are also other points that you might like to collect. Personal points are awarded for _your_ first geograph for a square. This map http://www.geograph.org.uk/mapbrowse.php?mine helps you find your personal green squares.
If you are the 2nd, 3rd or 4th visitor to a square and submit a geograph for it, you also get a repeat-visitor point for that. The best way to find which squares have had few visitors is the draggable map http://www.geograph.org.uk/mapper/ . You need to change the data overlaid on the Ordnance Survey map by clicking the blue '+' sign top right. Then select 'contributor depth'. This shows the number of different contributors to each square, so if it shows a '2', then you can get a 3rd-visitor point if you upload a picture for that square.
Finally, there are TPoints. They are awarded for geographs which were taken at least five years earlier and later than any existing ones, so you can get a TPoint for a current geograph if nobody has uploaded one taken in the last five years before you. If you enable the TPoint layer in the draggable map (again, via the blue '+'), you can see to which squares this currently applies. You can also get a TPoint for an archive shot which falls outside the periods five years either side of any previously uploaded geographs, but the map doesn't show this.
TPoint or 'Time-gap Point' is a new kind of point. A contributor can gain a TPoint by submitting a contemporary photo to a square that hasn't had a photo for 5 years. The aim is to increase the date range of available photos per square.
In general you will only get a point the first time you visit a grid square, and your photo is moderated as a "geograph". You may also get extra points if you are one of the first 4 people to visit the square. Subsequent photos in the same square will not get you any points, photos classified as "supplemental" will not get you any points.
Tpoints work slightly differently to the above: you get a Tpoint if you submit a geograph which has a time difference of 5 years (before or after) compared to other geographs in the grid square: So with Tpoints it may be possible to get subsequent points for the same grid square.