To get your lantus dose right, your bs should be between 100-105 first thing in the morning. That is if you are taken it around 22:00, before you go to sleep. This is the best time for most people. If it is lower than 100, reduce you dosage by 2units, if it is higher than 105, increase your dosage by 2units.
The first time that you use Lantus, it takes 3-7 days to find the right number of units for you.
For more info on useing Lantus, take a look at this site:
Lantus notes