1. Fuel properly. Breastfeeding means that you are providing calories & nutrition for a whole other person (allbeit quite a small one) - when I run, especially in the mornings, I notice that I need more energy than I used to so factor that in to make sure you don't have a big energy crash.
2. Try and time it so the baby won't need a feed half way round the course - that won't be fun for anyone. Breasts are super clever and can start lactating in response to the baby crying even before the baby has latched on!
3. Wear a decent sports bra. This is a tricky one as you can't easily feed in a normal sports bra, but I learnt the hard way that a feeding bra doesn't provide enough support. You can buy special feeding sports bras - generally American companies are more clued up on pre/post natal fitness wear.
4. Hydrate properly - breastfeeding makes you thirsty anyway so you need to ensure you're keeping your fluid levels topped up after exercise.
5. Be flexible & patient. Babies aren't predictable especially in the early weeks/months and they might need a feed unexpectedly which could scupper best laid plans. If you are exclusively breastfeeding then it can start to feel a bit overwhelming and like you'll never get out, but 6 months on I'm beginning to get some freedom and independence again. In the grand scheme of things, 6 months of cuddles on the sofa isn't going to impact on amateur runners & even Olympian Liz Yelling tandem breastfed her twins for 6 months!