A special needs adviser I once knew claimed there were more reading problems among children whose names began with d than any other initial.
Her theory was that these children learnt at their mother's knee to draw their special letter with a bump facing to the right; when teachers later told them d's bump faced to the left (and b's to the right) they became distraught. It's a disturbing thought: Darrens, Daniels and Damiens down-cast, dejected and demotivated - condemned by the devilish d to a lifetime of dyslexia.
To avoid this problem b and d should be introduced as far apart as possible d first. Emphasise kinesthetic learning through letter formation (d goes with c, a, o, g and q in starting with a c shape) and always finish it with a flick, which makes it visually distinctive from b as well as contributing to early joining. At the same time help children feel how the d sound is produced (tip of the tongue against the roof of the mouth) and associate it with a few memorable d words like dog, duck and dinosaur. After you've later taught b in the same multi-sensory way, help them seehearfeel the differences between the top letters.
Bd discrimination aside, however, d's really a doddle. The only thing to remember is that to keep a preceding vowel sound short, it doubles up, (eg rudder, ridding, and laddy as opposed to ruder, riding, and lady).