Are you thinking of doing the Tube Challenge? Visiting all 270 stations on the tube? Good on you! Here's a few tips and tricks for you. The rules can be found elsewhere.
FIND OUT ABOUT OTHER RECORD ATTEMPTS
There's several good videos of attempts out there on YouTube, and there's the ever popular Tube Challenge forum at tubeforum.co.uk/forum - have a good read and watch of these things, as they can provide useful tips and stories of challenges from others. I had two years of reading these, and they are immensely helpful.
It helps to know London above ground as well as below it. Are there two stations that are very close above ground? If so, perhaps you could run between the two to save time? Is it quicker to run it or to do it by bus? And know your bus connections. The 307 and a bit of a run on the end is far, far quicker to get to Cockfosters than the 384 that goes to the station but all round the houses.
KNOW YOUR RUNNING PACE
Be honest with yourself. Don't plan to make a 4-minute train if you know you can't make the run in four minutes.
Now for the specifics...
I simply cannot stress how important this is. Use London Underground's Working Timetables - https://tfl.gov.uk/corporate/publications-and-reports/working-timetables - these are more precise than Journey Planner and thus you can plan your journeys more precisely.
On the day, know where your door positions are. Especially in the rush hour, you want to be the first one off the train so you can beat the crowds. I would recommend Station Master for this.
You also need live departure boards ready and available in order to see what the speed you need to run at is. It also informs you of any delays. I use Tube Tracker. Cross-reference this with the WTTs (which you should also have on the go) and this is foolproof.
Now for the specifics...
This is the most important station, as it's a real pain in the arse. Trains to and from Kensington (Olympia), which has to be done by District Line, are so infrequent that you need to plan this. Either start from a slightly worse and aim for a morning train, or, if you're feeling cocky, start normally and aim for one of the two evening trains.
It's no secret that you should either start or finish your attempt in and around the "North West Corner" - the outer reaches of the Metropolitan Line, beyond the M25. Many people traditionally start at Chesham or Amersham. Watford's not a great idea because of the sheer amount of time it takes to go out to Chesham and Amersham and back again, although this may change when the Watford Junction extension opens.
THE OTHER OF THE "BIG THREE"
We've talked about Kensington (Olympia), so we will now have a look at the other two "big three": the Hainault loop and Mill Hill East. Prioritise and heavily research these timetables, are there are only three trains per hour to these stations, which means if you get it wrong you're very stuck. This is why planning can take months - so that you end up with a "perfect three", where you end up with five minute waits or smaller than that on the plan. Get these right.
WHY IS UXBRIDGE A PAIN IN THE ARSE?
Uxbridge is a turnaround station; there's nothing you can do except come back down the line. So if you miss your zero-minuter at Uxbridge or other similar stations (Morden, Richmond), you have to sit and wait.
THE FIRST RUN
OK, perhaps the final run if you're doing this the other way round, but general wisdom is to get out at North Harrow, and run. Run to either West Harrow or Rayners Lane. Other things have been tried, but they are rather peculiar. From West Harrow, you either follow the traditional Bakerloo Line strategy - West Harrow - Preston Road, turnaround to Northwick Park, get out and run to Kenton, where you go up to Harrow & Wealdstone and then back down the Bakerloo Line to a station of your choice, but no earlier than Paddington - or you go west towards Uxbridge. Alternatively, from Rayners Lane, you go down the Piccadilly Line to a certain place, which is less clear cut, although it's no earlier than Park Royal.