most pre-planned routes unfortunately assume you have a car. as you use public transport (well done!) you have to approach things about face by finding out about about public transport first. this can give you fabulous linear walks rather than going round in circles. this, of course, doesn't mean that shouldn't do circular ones.
however, following pre-planned routes is valuable for the experience you describe. you must always have a map with you and then, again experience, you will get an idea of what the ground is likely to be like.
i buy walk guide books as these give me an idea of where to go as these walks usually take in something that's interesting. i use these as a base with tracklogs to tailor distance (for after work walks), change the route in places to accomodate public transport and for general ideas.
frequently, walks start off with one route and when out think, what's that over there, and go take a look.
at first, always plan short because it's easier to add a bit on the end if you feel like it rather than suddenly realising it's getting dark and you still have an hour and a half to go. knowing where you are when it's dark can be a bit scarey until you get used to it and not knowing where you are when it's dark is no fun at all and is to be avoided at all costs (altough at times like that a gps unit can pay for itself but only used as a last resort).
be conservative with naismiths rule in mm. i find that 3-4km per hour to be a comfortable average walking rate - to that i add an hour and a half for food breaks, scenery, navel gazing and watching wildlife. a further half hour is added for the where the hell am i moments aka navigating. this gives a bit of leeway for making sure the bus isn't missed (especially if it's two hours to the next one and the knock on train effect).
plan yourself some easy routes (with nice clear boundaries like major roads) near home just to go out and navigate with the map to gain more confidence.
i assume you plot the trail routes into mm. print the map and a scribble copy of the map and write down on it the bits you were ok with and the bits you weren't. then study the map more and get a feel for what it is telling you.
not much help for this weekend i'm afraid though!
