I do think welcoming messages should ideally be catered to the person who is new. I would point a photographer to the photocontests and to @cryptoctopus' new photography curation initiative. Scientists I would point to #steemstem, developers to utopian-io etc. etc.
Since I take care of new scientists whenever I see them, this would be an example of how a welcoming comment of me usually looks like:

"Hey and welcome! (here usually goes a comment or question on what they've written)

If you plan posting scientific stuff, u should really use the "steemstem" tag and qoute your sources. steemstem's curators give well-written and rechered articles very nice boosts ;-) They also have a nice chat running.

Should you feel like reading a very well-written and extensive guide to the world of steemit, take a look at this one that I recently found, I can highly recommend it.

I'll also follow you, cya around!"