Half marathon strategy

Personally, I find an even pace is best, and if you're still feeling strong after 11 miles maybe then increase your pace.  If your running well, you should feel strong at the half-way mark but speeding up too fast at this point means you may struggle in the last few miles.

Don't try the "fast as you can" approach on a half as its too far and you will suffer. I did this recently and posted my worst ever time for a HM, as I ran at my original target pace despite not really recovering from a chest cold.

If you can keep an even pace throughout, you will find that you'll go past a lot of people in the last few miles who have over-cooked it.

My two fastest halfs were achieved by running a negative split. They were also the two that felt the best physically and mentally.

Conversely, whenever I've run a positive split I have felt like I'm hanging on at the end and just about fall over the finishing line.

The tricky thing about running a negative split is judging the relative speeds that you want to run in each half. I work out the average pace that I want to run the entire race and then add 5 seconds per km for the first half and subsequently subtract 5 seconds per km for the second half. That seems to work for me, you could be different.

Run as fast as you can without accumulating lactic acid for 11 miles. After that it doesn't matter.

Ran the recent Marlow Half marathon with negative splits. But then again so did most of the other runners. The first 5 miles being uphill has something to do with it.