This is something I’ve not seen much in KDE over the years, but these sorts of call-to-action posts seem to work.
Contributors from all areas could make more posts about crucial or beginner-friendly issues that they feel should get more attention and get them to Planet. This would have the additional benefit of letting others know what projects are struggling with.
I see two ways of going about it:
Help needed with X, Y and Z
Want to make your first contribution to X? Here’s a list of tasks to get started
I’m currently really busy, so I have quite a bit of “five minute items” on my todo list, some of which don’t really need that much requisite knowledge. Maybe it would be better to ask people on Discuss, so new developers could have a well-defined problem to solve.