The difference between the various rooms in chat goes way beyond the name of the room, each one has a different community inside. In some rooms, half of the participants swear like sailors, in other rooms letting a bad word slip is considered to be extremely poor form.
Some rooms love animated .gif files, others hate them. Some rooms tolerate a mix of languages, others prefer that everything be in English.
Self promotion in chat is not unlike anything else that is potentially taboo. Treat it like you would any other potential faux pas in a social setting - get to know those around you first, then gauge what's appropriate.
A friendly, on topic (as Martijn Pieters noted) link sent to someone that asked for a recommendation is generally going to be fine. Repeated links to the same thing may or may not be fine. Dropping into a room, planting a link and leaving is never going to be fine.
There's really no blanket answer here other than take the time to observe the community that you've joined, let them get to know you and then use your best judgement. When doing something that you're unsure of, be especially observant of criticism.