Here’s a really, really wonderful article (it’s actually a transcript of a lecture) that talks about tawheed, bida (innovations), dawah, etc.
The Shaikh gives some really great examples (don’t miss the one about the old hag and bida!) and clarifies some really important issues.
I learnt a lot just by skimming through it (now I just need to read everything again slowly).
Please do read it* (and the Q and A session too):
[HOJ students – You will really like this as it summarises the whole course.]
Islam is the Blessed Religion by Shaikh Muhammad Al-Aqeel