General points can be computed using the calc
library of tikz
. An expression of the form
($x!t!y$)
will find the point a fraction t
along the line from x
to y
. Combining this with drawing directives |-
and -|
for "vertical then horizontal" and vice versa gives:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
\node[rectangle,fill=blue!30,draw] (A) at (6,4) {Node 1};
\node[rectangle,fill=blue!30,draw] (B) at (0,0) {Node 2};
\draw[dashed,->] (A.south) |- ($(A)!.7!(B)$) -| (B.north);
\end{tikzpicture}
\end{document}
There are different ways to change the arrow. Firstly, just writing
\draw[dashed,->,>=stealth]
will give another shape. Loading the tikz
library arrows
gives plenty to choose between. Making the line thicker will also make the arrow more prominent, e.g. the combination
\draw[dashed,->,>=stealth,very thick]

Note that you could start your picture with \begin{tikzpicture}[>=stealth,very thick]
to make all arrowheads of stealth
type, and all lines very thick
.
For more control over the arrow, you can use the decorations
mechanism. In your case this could look like:

from the following code
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,arrows,decorations.markings}
\begin{document}
\begin{tikzpicture}[>=stealth,decoration={markings,mark=at position 1 with
{\arrow[scale=3]{>}}}]
\node[rectangle,fill=blue!30,draw] (A) at (6,4) {Node 1};
\node[rectangle,fill=blue!30,draw] (B) at (0,0) {Node 2};
\draw[dashed,postaction={decorate}]
(A.south) |- ($(A)!.7!(B)$) -| (B.north);
\end{tikzpicture}
\end{document}
See the pgf
manual for further details and constructions. Another illustration of arrow tips via decorations may be found at TikZ: Large arrow tips at the end of smooth curves.
pathortho
library that's demonstrated in Vertical and horizontal lines in pgf-tikz that does exactly this kind of thing. – Jake Jun 2 '13 at 13:10