Mentioned before but since this is more specific:
My first was the Thames Path, which I started because I live along it. Not massively interesting although beautiful in parts. I had to do that in two sections because it's not just my employer who gets fed up if I go off for too long, it's the boss I have to worry about.
My second was the Two Moors Way, which suffers a little from having the best bit at the beginning, unless you do it southward rather than north, which seems to be the conventional route.
I then did the Cambrian Way in three sections (it's around 300 difficult miles). Absolutely wonderful walk.
I also attempted the 6 Shropshire Summits but that was around the time of the Foot and Mouth thing so found some parts closed.
Similarly, I've done sections of other LDPs such as the SW Coast Path, but haven't completed them because I simply don't have the time (looking forward to retirement but it's still some way off).
I have also done sections of some of Europe's GR routes, but to do the whole lot of many of them is a major undertaking due to their length.
Plans? The Coast to Coast as well, but perhaps the West Highland Way too. I've thought of Offa's Dyke but that might be a bit of a let down after the Cambrian Way. I've also done some planning for the Cleveland Way but abandoned the idea due to lack of places to stay on the route. However if my latest lightweight camping project works out (see another post) then this could be resurrected:
The problem I have with LDPs is that there are two opposing options. One is to travel light and stay at Youth Hostels, Pubs, B&Bs etc., but this gives very little flexibility. For example if you find that you've overestimated how far you could go in a day due to the difficulty of terrain (or because you took summitzero's advice, as I do, and took the time to enjoy what you see) , it can throw out all the advance bookings you've made. The alternative of hoping to find somewhere to stay when you get there can also be a problem when you find that the place you were expecting to get to stay at has closed or is full.
I'm a great believer in using the Youth Hostel network, however the YHA has this year instigated a large closure program, largely targeting out of the way hostels where of course there is nowhere else to stay.
The second option is to camp, which gives much more flexibility, but of course adds significantly to the weight you're carrrying when you add in a tent, sleeping bag, cooking gear, lighting etc. And of course you miss out o the warm and cosy bed for the night.
The best advice I'd give therefore is to plan to as much detail as possible. Get the guide book and trawl the internet. Examine the OS maps in detail to glean as much info about the terrain as possible - we make this a bit more fun by having 'planning' meetings on Sunday evening in the pub. Book accommodation in advance if you can, but this means you do need to be certain you can cover the distances you plan for each day. And build in rest days, for example over a week I would set a short 5 mile section mid-week so you get the afternoon off.
Above all travel light, and if a piece of equipment can have more than one use then go for it. For example use resealable gas cylinders so you can use one for cooking and then for lighting. I also have a cookset with a loop handle (as opposed to a panhandle) which I acquired for a trip to Greece where the primary water supply was wells, so I could tie some string to the handle and use it to raise water.
I could go on but that will do for now I think, don't want to bore anyone.
S.