I guess a good place to start is, " buy a sewing kit" whether you get a complete kit, or select what you want.
get some quality needles, and several common thread colors.
like Black,Navy,White,Brown,Red,etc. and take every chance you get to collect buttons.
find a good sewing store. they will have all you need. and new buttons, buckles,and other stuff. you would be surprised.
if you are really keen, buy a sewing machine, (i have 2) play with it and learn to use it. then check on Youtube how to do basic repairs on your own.
you can then replace buttons, re-sew split seams, shorten pants, and make your own pocket squares as a start. all the info you need is online, a good kit will enable you to maintain and repair your clothes.
- so you need not pass a suit with a ripped lining etc.
Most (not all) of my kit:
I started with a "Snoopy & friends" sewing kit (on sale) and added to it.
items like scissors, thread picker, slim box knife, more threads, and a chalk triangle. plus a measuring tape, pins&cushion. make basic repairs simple.
Getting a good sewing kit is really worth mentioning. Just bought one from Amazon http://www.amazon.com/Portable-Travel-Sewing-Kit-Beginners/dp/B00GR0ESK0/ref=pd_sbs_ac_31?ie=UTF8&refRID=1T3QYMF01CBFX8CYC8DF and it really decent for the price point.
Save me quite a few bucks.