I have a trigger (code below) that works for some updates equal to the where statement but not all. Very new to triggers so I'm wondering if there are any initial things I need to look for.

CREATE TRIGGER tr_hold_complete ON CallsHistory
for INSERT AS
insert hold_complete
select ins.AddedDT, ins.fkey, ins.actiontext,
ins.subactiontext, con.emailaddress, ca.loggeddt,
(con.forename + ' ' + con.surname) as contactname,
ca.summary, ca.notes,co.coordinator, co.coordinator,getdate(), ca.status
FROM inserted as ins join calls as ca on
ins.fkey = ca.callid join contact as con on
ca.contactid = con.contactid join company as co on
ca.contactid = co.contactid
where ins.actiontext = 'hold' and ins.Subactiontext = 'completed'

This trigger is defined for fire only on insert. You mention 'update' which I literally take as meaning you need to fire the trigger BOTH on update and insert. Also, make sure the literals you are checking against the columns are the proper case (could those columns have uppercased data?). Something else to consider is the joins. You may have to specify an outer join (are you assured that there are corresponding data in calls, contact, coompany?).