Improving my times

I ran regularly up until 2009 when a serious leg injury meant I was unable to run for 2 years. Since then I was blighted by shin, knee and ankle injuries until October 2012.

I finally seem to have overcome my injuries and am running a 2hr 10m half marathon. My aim for this year is to knock that down to 1hr 48m and over shorter distances (up to 3miles) I can now maintain that speed.

Other than simply upping the distance, are there any tips to increase speed up to 13.1 miles?

depends what you're currently doing for that 2hr 10.

if you're running 15miles a week however you fancy, improvement will be simple.

if you're doing 60miles a week with 2 quality sessions tailored to your ability, along with a very long slow run on the weekend, it'll be less easy.

1:48 for a HM is 8'15" min/mile, so I guess you've derived your target time from the pace that you can maintain?

Trying to run at 8'15" pace in training and build this up to 13 miles is a poor training strategy.  Nearly all training schedules include longer slower runs to build endurance with shorter high intensity runs (e.g. intervals & tempo sessions) to boost speed.  They tend to vary the ratio & frequency of these, but splitting your training into speed-specific and endurance-specific running is the foundation of them all.

Using the Mcmillan pace claculator, the 1:48:00 HM is equivalent to  48:27 mins for 10k.  So you would be better aiming to break the 10k target first (7'48" min/mile pace), and then build your endurance to enable you to complete the HM in 1:48:00.  

As Stevie G has said, there's no real shortcut to improving your time - you need to put in the miles, but if you train smarter you can maximise the benefit from each mile that you run.