According to your snippet, increasing dopamine in the brain will decrease latent inhibition.
Dopamine is produced in the body from the chemical L-dopa.
Wikpedia states that dopamine will not cross the blood-brain barrier, so to increase dopamine levels in the brain L-dopa must be used.
Wikipedia also says that there is a herbal extract containing L-dopa called velvet bean. Wikipedia provides another solution, which uses the amino acid Tyrosine which is the precursor to L-dopa, as well as dopamine, adrenaline and noradrenaline. So, be aware that use of this amino acid won't just increase your L-dopa levels.
A red herring I found were melanocytes, which produce L-dopa as part of the melanin synthetic cascade, however the amount produced is negligible.
Aside from chemical alteration, what lowering latent inhibition entails is ignoring fewer things. Making cognitive filters less strict. Essentially this becomes a problem of attention - how to attended to things that haven't helped (haven't been reinforced) in similar situations.
It just so happens that there is a psychological phenomenon called latent learning. The classic experiment is one where some rats are allowed to roam freely in a maze with no objective, while the rest aren't. Later, when each rat is put into the maze to find food, the ones that have previously been in the maze find food more quickly. The rats learnt about the maze without reinforcement.
I would therefore suggest that to decrease latent inhibition you must deliberately pay more attention to your surroundings.