I just finished two books on how to deal with tarot cards, and I
had done a few readings for myself.
However, when I do my readings for my dad, it is not very
accurate. The first reading I had done for my dad is still all
right, but the second reading was totally off-the-point. Arggh!
Hey~
I think that exploring tarot is a good thing. Do know that
reading a book about cards and actually having experiences with
them are quite different. Depending on the books that you
have about the cards- it could make a whole world of
difference as well.
You are just starting out, lower your expectations. 
Do not strive for 100% accuracy.
I feel that in order to be accurate, you will need to find your own
voice. Your way of relating to your cards.
When you say that your reading was totally off the point, was it
addressing an issue that your father may not be too forthcoming
about?
Or was it talking about an altogether different issue from what you
were asking?
Did it make sense, or was it totally nonsensical?
In retrospect now, did that "off-the-point" reading now make sense
in regards to your situation back then...?
All of these are different situations that you may encounter, and
will result in a different explanation and advice to proceed.
If you do encounter any more issues, feel free to enquire
around. People here are generally helpful (if you can find them
online, in time). 
Do remember-- practise safely, and do not dabble with
anything beyond your scope. 
(Beginner's luck can only cover
you so far- beyond which you had better know what you are getting
yourself into...) 
Until then, lucks with your exploration, and be safe~
Take care! 