While your partner is going through pregnancy the most important thing to remember is to be there for her, she will go through a range of emotions and have ups and downs but as long as you understand that it is not abnormal and you dont have a go then you will be fine. I found that you have to have a sense of humour and helped in any way that I could then it was the best way forward.
Another thing to remember is that your partner will possibly be feeling scared of what lays ahead and if you do your research then you can talk about any fears that she may have. Dont be afraid to say I dont understand.
The books will tell you what to expect in each tri-mester however everyone is different so dont take what the books say as a definate and expect everything to happen as it says, when it says.
It is true what they say however about the tiredness, your partner will become increasingly tired and this is where simple things you can do will help, also chances are your partner will be very uncomfortable sitting, standing, lying down and a good idea I had was to go and get a triangular pillow which my wife found to be a great help, alternatively you can get the body pillows which can be a an amazing help Search Amazon.com for pregnancy pillows
Once you are past your first couple of months then it is time to start thinking what you might need - dont just rely on your partner to think of everything as she has enough to think about!
Some of the basics you will need are;
Steriliser and bottles (if you are bottle feeding from birth)
You dont need to start off with much as it is best to wait until closer to the birth as you will have an idea of size of your baby and if you want to know the sex then you can think about pink or blue.
It is also a good idea to think about where you intend your little one to sleep at this point as this can affect what size crib/cot you choose.
Think about choices of moses basket or crib/cot but dont rush out and buy it if you are supersticious and believe that having things like that in the house is bad luck before baby arrives.
Search Amazon.com for baby crib
Search Amazon.com for moses basket