Auto potion

Another problem people have with staying alive is the use of their healing
items. People think they're cool just using HP or MP recovery herbs when they
see fit. That's all well and good, but if you find that you're dying more than
once per session, you may want to consider turning on auto potion.

First, press "T" to bring up the menu. Click the auto-use HP herb button and
set a desired life total at which you want to use a healing item. On
characters with self heal, I set it at 35%, and without at 45%
Leave the potion delay on, unless you want to be using two or three heal herbs
at a time when you only needed one.
Select the belt slot it's in (you can set it to f4-9 if you really don't want
to be bothered with it), then press confirm to turn it on.

I recommend doing this with mana as well, but at a much lower number, like 20%.
The common argument you'll hear is this "I'll decide when I want to use my MP
berries! I don't want to overuse them!" But think about it. If you're down
to 15% MP, are you going to sit down and wait for the whole bar to charge?

A problem with this, however, is that you'll find yourself using skills with
much less inhibition. This may lead to the purchase of more MP berries than
before, but they're only 50 gold apiece, and you pick up about 100 gold from
any monster on the first continent.
http://www.gamefaqs.com/computer/doswin/file/930711/43300