If you want flexibility (at the expense of a bit more complexity), look into LVM. With this, you can adjust your filesystem sizes as needed, whenever needed. You're no locked into the partition sizes you guessed at install time.
Some people don't really even partition - having just / and swap. Others create hard partitions for each filesystem. Others use LVM. There are pluses and minus for each approach. As you move from no_partitioning -> hard_partitions -> LVM your flexibility increases, but so does the complexity. Decide which method you are comfortable with, and go for it.
FYI, below are two systems I have (Debian). You can get some idea of OS filesystem sizes for my computers from this. Yours may vary of course. I left out other filesystems I have that are too installation-specific to be meaningful (e.g., /music, /photography, /videos, /backup, etc.) I do not use /home for much, preferring to use seperate filesystems to store stuff like music, photos, etc. Personal choice.
Code:
$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda7 897M 139M 711M 17% /
/dev/sda5 45M 18M 24M 43% /boot
/dev/mapper/vg0-usr 2.8G 1.9G 896M 68% /usr
/dev/mapper/vg0-var 1.9G 882M 894M 50% /var
/dev/mapper/vg0-opt 237M 155M 70M 69% /opt
/dev/mapper/vg0-tmp 469M 8.1M 436M 2% /tmp
/dev/mapper/vg0-home 94M 58M 33M 64% /home
Code:
$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/hda8 287M 147M 126M 54% /
/dev/hda9 30M 7.6M 21M 28% /boot
/dev/mapper/vg_linux-usr 3.3G 2.8G 448M 87% /usr
/dev/mapper/vg_linux-var 1.4G 545M 823M 40% /var
/dev/mapper/vg_linux-opt 614M 517M 78M 87% /opt
/dev/mapper/vg_linux-tmp 94M 4.1M 85M 5% /tmp
/dev/mapper/vg_linux-home 98M 81M 14M 86% /home