Like everything else, school assemblies have really changed since we were at school (well, yes, in some cases they may be frozen in time, but it’s almost definitely a lost opportunity if they are!) If you’re only starting to get to know your local school, you definitely need to find out their current practice – and if you’re going to be helping lead an assembly, ask what they do (and don’t) want from you.
But there are also some good articles to read like http://www.syls.org.uk/get-started/a-time-to-reflect-or-religious-observance-ro.html
The Schoolswork website has some good practical advice at http://www.schoolswork.co.uk/ineedto/plan-an-assembly/P0/ - but do remember that we don’t have “Acts of Worship” in Scottish schools, so jump over that section.
And type in Assemblies to our Resources search engine, for lots of great ideas.