Do you drink alcohol or do any drugs through the day or before bed? They could have an impact on dream recall, if not my only advice is to start keeping a dream journal which most people will say.

Another thing you could try is writing down what you did during the day before bed in a journey or on a say a word document on a computer. It made me go from 1 dream a night or every other night to usually at least 3, possibly more but I've been slacking in writing them down. It also makes me wake up after each dream which is very useful for WILD, DEILD and WBTB. Hopefully it will work as well for you as it did for me, but I always write what I did during the day before bed and everytime I do I have a huge increase in dream recall and vividness.