Rent a room in any inn and close the door when u get in. Or simply use an empty room in your own house. There must be a bed and a door to work with.

Notes:
If you level up while performing this, add points to intelligence and willpower to make your magicka regenerate faster. Turn off autosave after sleep to speed the process up.

Conjuration:
Time to Master = About 30 to 45 Minutes.
Simply summon skeleton over and over, and when your mana runs out go to sleep for one hour.

Alteration:
Time to Master = About 30 - 45 minutes.
Repeatedly cast Easy Unlock Spell on the door to the room. Again, when your magicka runs out, simply sleep one hour to regenerate it.

When your willpower and intelligence are high enough, you will be able to cast these spells without sleeping, speeding up the process even greater. You can gain 10 to 15 levels with this trick depending on where you start from.