Skills:
Magic Lore
Meditation
Water Magic
Agility
Trade
Constitution
Air Magic
Parry
Ok you'll start off dropping points into Magic Lore, and Meditation. I like to keep this up till they're around level 10 each. Once that happens, I catch Water Magic up to my level. From there on in, I keep Water Magic maxed out, and do so until after level 51.
By level 53 or 54, you should have skills that look like this (before item bonuses)
Magic Lore 50
Meditation 50
Water Magic 51
Agility 10
Trade 1
Constitution 10
Air Magic 1
Parry 1
These numbers might be off by a couple points. There may be a few points left over to stuff a couple into parry.
From level 53 - 75 is when we're going to work on Agility, Parry, and Constitution. Over this period we'll gain 88 skill points which should get those three skills in the mid 30's ranges. Apportion points how you see fit according to equipment (for instance if you find a shield with a huge constitution bonus, place points primarily into Agility and Parry).
From level 76 - 100 we're going to put all our points into Trade, to pump it to level 100.
From level 100 on, we'll mostly be maintaining trade at our level, and pumping up Air Magic, and making additions to Constitution, Agility and Parry.
With the exception of Trade, you'll want to place your points into the skills you will feel to give the largest pay-off. The skill growth rate generally drops to abysmal levels post 50, which is why I chose that as a bench mark for Meditation and Magic Lore, and why you'll likely use them for the last 4 skills as well.
Update: Skills at Level 108
Magic Lore: 70
Meditation: 50
Water Magic: 51
Agility: 27
Trade: 108
Constitution: 36
Air Magic: 2
Parry: 54
Just a little look at the route I've taken my current HC Ice Shard Mage. For the next while I'll be working on Magic Lore, Constitution, Agility and Parry. Of course, maintaining trade at my level is a constant part of this throughout the rest of the game as well.
Combat Art Selection:
Ice Shard
Ghost Meadow
Stoneskin
Flameskin/Whirlwind/Shield Wall (pick one to suit your tastes, I recommend Flameskin)
Gust of Wind
Phase Shift
Ring of Ice
From the start you'll be using Fireball as your primary attack spell. If you get really lucky in an early quest and get another Fireball rune, feel free to read it, but I wouldn't recomment using more then 1.