Hi, I've been exclusively pumping for my daughter since birth (now 7.5 months) and I worked really hard at the beginning to get a good supply. These are the things I have found work best...
Fenugreek tablets - you can get them in Holland and barrett, but I got mine from Amazon. A bigger bottle at about 2/3 of the price. Take 3 tablets, 3 times a day. It sounds like a lot, but you need to be taking a high dose. You might notice your sweat starts to smell a bit strange. Either a sweet curry smell, or a maple syrupy smell. This is normal!
Drinking lots of water. Keep well hydrated.
"Power pumping". This mimics cluster feeding. You have an hour, where you pump for 10 minutes, rest for 10 minutes, pump for 10 minutes, etc. I have found this really effective. Try and do it once a day.
Make sure you pump at least once in the middle of the night. Milk production is at its highest between 1am and 5am, so try and pump once between these times.
Eat lots of oats, porridge etc. Something in it boosts milk supply.
What sort of a pump you are using? I use a double electric pump, and it is a god send. Invest in a good pump if you can.
Massage your breasts as you pump, really give them a good old squeeze, and when you have finished with your pump, try and hand express to get anything extra out. I often find I can get a few more mls out by hand.
Good luck, message me if you have any questions!