How can I draw a grid of help lines like \draw [help lines] (0,0) grid (3,2); but use other base vectors (not (1,0) and (0,1)) instead?
E.g. choosing (1,1) and (1,0) should ideally give me a grid something like this

How can I draw a grid of help lines like \draw [help lines] (0,0) grid (3,2); but use other base vectors (not (1,0) and (0,1)) instead?
E.g. choosing (1,1) and (1,0) should ideally give me a grid something like this

You can use the xslant=<factor> where <factor> is, of course, a number which in degrees will be the inverse cotangent of <factor>:
\documentclass[tikz, border=2mm]{standalone}
\begin{document}
\begin{tikzpicture}
\begin{scope}
\clip (0,0) rectangle (3,2);
\draw [help lines,xslant=1] (-5,-5) grid (5,5);
\end{scope}
\draw (0,0) -- (45:1);
\end{tikzpicture}
\end{document}
cmkey does the same (you can read about it on the manual) – percusse Nov 09 '16 at 13:37