Toby A is right. You've got to monitor yourself. When your arms are tired you won't hit the ice hard enough to get secure placements. Watch out for feeble pecking, especially with your weaker hand.
Five remedies:
1. Train. Get stronger arms and hands. Can you think of *any* climbing situation where your problem is going to be that you're too strong? No, me neither. When you're at home, put your axes over a tree-branch or a piece of paintwork you don't care about and do pull-ups on your axes. See how many pull-ups you can manage before your arms turn to celery. Remember how many it was before you commit to something vertical on a real climb.
2. Mechanical advantage. Always swing the axe from right down the handle-end, and let the weight of the axe do the work.
3. Don't over-grip. If you do you will pump out in no time.
4. Use your feet as much as possible and your arms as little as possible. The steeper the ice, the harder it is to use your feet-- and the more you need to, unless you're as strong as an ox.
5. Climb in an A shape where you're hanging off ONE axe and free to move the other. Not in an H shape where you're hanging off BOTH axes and can't move anything. In this very good little video Matt Wade calls it building a triangle.
Post edited at 21:38