One thing that drives me up the wall is when someone takes to slaying every instance of 'was' under a misguided belief that it's constructing 'passive tense'. A fair few uses of 'was' are not even close to passive tense... It's a bit like the Holy Crusades...
The best trick I heard is if you can stick a 'by someone' in there somewhere, you know it's passive.
Let's take an example: 'He was moved by her.'
This is long passive form.
The 'agent' and 'patient' are the technical words for determining things (different to 'subject' and 'object'). Agent does the action and patience has the action done to them. In passive, the patient is the subject. So the 'he' in "He was moved by her." would be the patient, and the 'her' would be the agent.
The active form of this would be: 'He moved her.'
Here we see the agent taking up the subject slot 'he' and the patient in the object slot. It's the reverse of the passive above.
Now, a confusion some writers have is with short passive. Any long passive can be shortened to remove the 'by someone'. In the example above, we could shorten to 'She was moved'.
Three words. So what's the difference between this and something like 'She was dead'? Only one word is changed, but that word is crucial. In our passive example, we have a verb participle 'moved'. In this second example, we have an adjective 'dead'. No action is occurring to anyone in the second example at all. It's not passive.
People also get confused with the passive and the past progressive. An example of past progressive that looks very similar to our passive example is: 'He was moving.'
But can you stick in a 'by someone' into this? No. There's no patient receiving the action. Only an agent doing something.
To have a passive past progressive (rare, but technically viable), you'd have to have something like:
'She was being moved by him.'
Where again, you can see the passive structure: patient ('she') being acted on by agent ('he').
So there are some of the subtleties of the word 'was'. Please don't get confused, and treat it with the respect it deserves!