As with most aspects of angling, your choice of line should be based on the type of fishing you are doing.
For general beach fishing over clean ground the ideal main line is 15lb (0.35mm) with a suitable shock leader. Some anglers prefer to use 18lb ( 0.37mm) to give them a little more security, but this will reduce your casting distance. If distance is very important then its possible to get away with 12lb (0.32mm). The main risk with using lower diameter lines is that the slightest rub or nick can reduce the strength and result in break offs. Our most popular brand of line for main line is Ultima Sea Strike, closely followed by Ultima Red Ice, both of these brands are very well priced and offer consitant quality.
For rough ground fishing there are two options, the first is to simply step up the main line to 18 - 25lb with a shock leader. This will help reduce loss of tackle from snags, but still has a weak link in the leader knot, which will virtually always be the breaking point in the event of getting snagged. The second option is only really possible when casting distance is not important, this is to use a heavy line from 30lb -40lb straight through, so without a shock leader. If using this method its essential to avoid power casting as 30lb line will break if a 5oz lead is cast full power, but for an overhead thump it is generally usabe. This method if coupled with a rotton bottom and weaker hook lengths (15lb-20lb) will see you getting most rigs back even in the snaggiest of spots. Again Seastrike or Red Ice are probably the most suited line.
Shock leaders are essential for virtually all sea fishing situations, they absorb the shock of casting and prevent weights and rigs being sent of in all directions during the cast. There are two types of shock leader, the tradiitional method is a length of 50lb-80lb line tied to the end of the main line, its essental that the length is long enough to have 6 winds around the spool whilst casting. The more modern method is a tapered leader, this is a specially made length of line that has been tapered to go from 15lb to 60lb or similar, so one end is 15lb and the other is 60lb and it taperes along the length. This method is far more costly than the first, but offers a much tidier smaller knot at the joint between leader and main line. I would suggest Ultima Powerflex Tapered Leaders as being very good.
Rig bodies should be made from line of similar strain to the shock leader as they are going to be subjected to the same tensions during casting.
Colour of Rig body is a very personal thing, some anglers swear by yellow, claiming it catches more fish, others will only use clear, claiming anything else uis visable to the fish. I think in most UK shore situations the water is too dirty for it to make much difference, I personally always use clear, but thats more habit than anything else.
Ideally a rig body should be supple and low stretch, an ideal choice is Ultima Powerflex.
The strain of hook lengths is very dependant on the type of fishing you are doing, I generally use 20lb for most match fishing, and step upto 25lb or even 30lb for bigger fish.
Like with the rig body I always use clear, but again its very much what you feel comfortable wth, I know succesful anglers who only use red hook length!
As with the rig body, suppleness is important, this makes the presentation much better and allows any kinks from tagles with fish to be easily pulled out. My favourite is Amnesia line, or Ultima Memorx