Dear redkitty,
Just a small request before we begin. Please use proper capitalization. It makes reading and answering questions a lot easier. Strangely enough, our brains recognize shapes as well as individual letters. So we can process properly written text easier and faster. Also, cant become can't and so on.
As fas as tenses are concerned, you might wish to review this
Verb Tense Chart.
Let's look at your specific examples.
I have never thought OF it before. Present prefect. It begins in the past and leads to and including the present.
Me: I think you might wish to check online sources to assist your learning.
You: I have never thought of that before.
Next example.
I had never thought OF it before. Past perfect. It describe a past event or condition completed before another event in the past.
Let's look at some other examples.
1) How long have I lived here? I have lived here for 8 years. (Present Perfect)
2) I had lived in a small town before I went back to school. (Past Perfect)
3) I have been going to the gym on a regular basis for several years now. (Present Perfect)
4) I had a heart attack several years ago, which caused me to lead an active lifestyle. (Past Perfect) [just an example, it is not true]
5) They have been boyfriend and girlfriend for several years. (Present Perfect)
6) She had called him before he wrote the letter. (Past Perfect)
Please review the Verb Tense Chart shown earlier.
Hope that helps.
MountainHiker