OK - this is more homework for you, so I'm not giving you the answers fully - you'll have to do some thinking for yourself.
How big a volume would you expect to have for a PCR (for 1 tube)? - so what sort of volume would you be pipetting for the primers (ml? l? ul? nl?)?
uM is micro mol per litre, how many pmol of primers will be in each reaction? And what volume would that work out to be?
Serial dilutions - you could do 1:10 dilution or any other multiple to get it to a pipettable volume (0.5 ul and above). 1:10 and 1:2 are the easiest as they are kind of intuitive (multiply by 10 or 2 respectively)
For dilutions the best equation to use is Vi x Ci = Vf x Cf where V and C are volume and concentration and i and f are initial and final respectively.