Start with the Rs. Understand that in most British accents speakers don't roll their Rs (except for those from Scotland, Northumbria, Northern Ireland, and parts of Lancashire), but not all British accents are the same. For example, a Scottish accent varies greatly from an English accent. After a vowel, don't pronounce the R, but draw out the vowel and maybe add an "uh" (Here is "heeuh"). In words like "hurry", dont blend the R with the vowel. Say "huh-ree". Pronounce U in stupid and in duty with the ew or "you" sound. Avoid the oo as in an American accent; thus it is pronounced stewpid or commonly schewpid, not stoopid, etc. duty would be pronounced dewty or more often jooty. In the standard English accent, the A (for example, in father) is pronounced at the back of the mouth with an open throat—it sounds like "arh". This is the case in pretty much all British accents, but it's exaggerated in RP. In southern England and in RP, words such as "bath", "path", "glass", "grass" also use this vowel (barth, parth, glarss, grarss, etc.). However, in other parts of Britain "bath", "path", etc. sound like "ah".
Belinda