When looking for Dragonflies/Damselflies, it is best to go on a hot, sunny day. 
A cool overcast day can be very disappointing. 
Personally, I tend to come here later in the season, between June and August.
The hawkers and darters are around feeding and resting.
The Norfolk Hawker was spotted mating here in 2023 and my thought is that this species will start getting a strong foothold on the levels over the next few years.

June
DRAGONFLIES: Brown Hawker, Scarce Chasers, Black Tailed Skimmers

July / August / September
DRAGONFLIES: Brown Hawkers (July), Southern Hawkers, Migrant Hawkers, Ruddy Darters, Common Darters

NB The list above just names the key species during these dates and is not a complete list.

Route
The site is generally good all over and all species can be seen at any point.
The walk along the grass track on the southwestern edge of the reserve to the viewing screen at the end is worth doing.
This track has a rhyne on one side of it and a tallish hedge on the other side.
Dragonflies love feeding along this area as well as looking for mates along the river.
It's a very pleasant stroll along here.

Flat / Mixture of hard core tracks and grass tracks / Hardcore track is generally good, grass track uneven.