Figure placement can be tricky and depends on what is surrounding it. As a major resource behind TeX's algorithm, read How to influence the position of float environments like figure and table in LaTeX?
In this instance, you could use the following setup:

\documentclass{article}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{graphicx,caption}% http://ctan.org/pkg/{graphicx,caption}
\begin{document}
\lipsum[1-2]
\newpage
\noindent%
\begin{minipage}{\linewidth}
\centering
\includegraphics[width=0.7\linewidth]{example-image-a}
\captionof{figure}{This is a caption}
\end{minipage}
\vfill
\newpage
\lipsum[3-4]
\end{document}
The idea is to avoid using a floating environment like figure, since you don't want TeX to make the placement. Instead something like a minipage works with a "fake" \caption.
Technically you don't need the entire caption package, as \captionof is all you're using here. So, using the capt-of package would also suffice. Also, there's no need here for the minipage environment. However, to contain the \centering alignment to a group, the minipage helps.
lipsum mere provides dummy text, Lorem Ipsum style.
For a more automated way of inserting the figure top-aligned on a separate page, use the afterpage package to insert it. The following MWE shows this:

\documentclass{article}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{afterpage,graphicx,caption}% http://ctan.org/pkg/{afterpage,graphicx,caption}
\begin{document}
\lipsum[1-2]
\afterpage{%
\noindent%
\begin{minipage}{\linewidth}
\centering
\includegraphics[width=0.7\linewidth]{example-image-a}
\captionof{figure}{This is a caption}
\end{minipage}
\newpage%
}
\lipsum[3-7]
\end{document}
[t]as the option? – Sigur Apr 26 '13 at 02:25hit tries to insert the imagehere(near the position where the command was inserted). If is not possible then it tries the second option. – Sigur Apr 26 '13 at 02:28[ht!]with[t!]? – Mico Apr 26 '13 at 02:38