Graphviz for simple diagrams that can represented with basic shapes. PlantUML for sequence diagrams, state machines and the likes. Powerpoint/Keynote for thin

Graphviz for simple diagrams that can represented with basic shapes. PlantUML for sequence diagrams, state machines and the likes. Powerpoint/Keynote for things that are presentations - and usually I will export one of the above formats as SVG, clean it up a bit, turn into PDF and drop into the slides. As a general rule all my diagrams must be vector based, and no bitmap objects should be embedded. Confluence with Graphviz and PlantUML plugins for placing diagrams into documentation. This also gives more granular version control. Other diagrams may also end up in source control with the product itself. Occasionally I have ASCII art embedded in source code, nearly all of this is hand cranked as I've yet to find tools that work for me. Almost always this is formatted to show up in generated documentation. But most importantly is having consistent design elements - spend time having colour palettes that are consistent, typefaces and type positioning that match, that shapes and layouts are as consistent as possible. Having templates, colour palettes, and snippets help. Finally, understand basic colour theory, typography and layout. Looking at graphic design visual porn (Behance is a good starting point) after knowing the basic rules will hopefully give meaningful inspiration.