Any tool in particular that you suggest to make diagrams? Or maybe just pen and paper?
I tried StarUML 2 and it's ok but I found it slightly clunky (it also does not have a realtime collaboration feature as far as I know, that would be nice to have when your team is remote IMHO)
White board it, modeling should be a group activity. Everyone should contribute their ideas so we can converge towards one mental model. If I'm working with 1 or 2 developer, we can cluster around a table and use pen and paper. I only use professional tools if I'm going to be giving presentation or wish to store it for long term.
In Linux there is modelio, and there is also Visual Paradigm which is available on most platforms and has a free community edition.
Try https://www.lucidchart.com . It is slick, has real-time collaboration, has UML (including via markup) and lots of other diagrams. Freemium that allows you to do most things.
Unfortunately lucidchart is only a drawing tool (no model validation, no documentation nor code generation).
If you need both real-time collaboration and real UML tool, you should try https://www.genmymodel.com
I use doxygen mixed with dot for rendering the UML. Mostly for looking over the layout of the code after it's written to make sure there aren't any lines/dependencies that there shouldn't be. The nice thing is that this leaves you with both an HTML doc and UMLs as PNGs. I haven't found any great tools for creating UMLs ahead of code... like for many here, that seems like a recipe for outdated/mismatched code to UML in the long run.
I tried StarUML 2 and it's ok but I found it slightly clunky (it also does not have a realtime collaboration feature as far as I know, that would be nice to have when your team is remote IMHO)