Hi Julia!

in no particular order:

• learn how a relational database works (this is always useful)
• learn how HTTP works in general
• learn how to debug code in one language (it's pretty much the same in others, you can recycle most of the knowledge)
• be familiar with the command line
• know how to find code (either using your IDE or grep on the command line)
• knowing the basics of regular expressions will get you far (also to find code in the previous point)
• know how to find solutions using a search engine
• know how to operate git (I would say any source control but git is the de facto standard so you might as well start with that)
• ask questions, especially if you think they're not worth being asked
• learn how timezones work (not kidding, lots of devs are still fuzzy on these)
• learn how unicode and utf-8 work (same reason for timezones)
• have a general idea of how caching (CPU, in memory, disk, HTTP) works as a concept

notice that other than git I didn't specify any particular tool, this is because it's stuff you will bump into no matter which languages or tools you'll end up using.