The procedure is pretty much the same like everywhere, e.g. in Vientiane. But, compared to Vientiane, there are at least two things better. First, there are only a few applicants and not hundreds. Therefore it's all much faster done. So, it's not really worth to come long before opening time and to wait outside. They even open the gate before the official opening time - in contrast to Vientiane.
Second, they don't ask for a photocopy of the passport and Malaysian visa. One fills in the usual form and - most important - pays the fee. The fee is 110 Ringgit; more expensive than elsewhere and only possible in Ringgit; they don't accept Thai Baht.
The whole blunt procedure takes two days. On the first day in the morning one applies, next day in the afternoon one is granted to receive the passport with the new visa.
Busses from Chinatown to Jalan Ampang are frequently, for example bus no. 79 or 28.