documentclass{article}
usepackage[sf,pagestyles]{titlesec} % make section headings sffamily
% make headers sffamily
newpagestyle{main}[sffamily]{
    sethead{thepage}{}{sectiontitle}
    }
pagestyle{main}
usepackage{titling}
% make titling elements sffamily
pretitle{begin{center}sffamilyLARGE}
preauthor{begin{center}
            largesffamily lineskip 0.5em%
            begin{tabular}[t]{c}}
predate{begin{center}sffamilylarge}
usepackage{abstract}
% make abstract title sffamily
renewcommandabstractnamefont{sffamily}
usepackage{kantlipsum}
title{A title}
author{An author}
date{today}
begin{document}
maketitle
begin{abstract}
kant[1]
end{abstract}
section{A section}
subsection{A subsection}
kant
end{document}

documentclass{scrartcl}
usepackage{kantlipsum}
title{A title}
author{An author}
date{today}
begin{document}
maketitle
begin{abstract}
  kant[1]
end{abstract}
section{A section}
subsection{A subsection}
kant
end{document}

usepackage{sectsty}

begin{document}
allsectionsfont{sffamily}
[...]
end{document}