1) Always replace your mascara every 3 months. This is the most hygienic replenishment time for all eye makeup products. Plus, it ensures your mascara never gets too dry and clumpy.
2) Always let mascara set (but not dry!) between applications. Two coats of mascara should always be applied, but never more than that. Wait 10 seconds for formula to set before applying second coat so lashes won't clump.
3) Never apply before liner. Your fresh coats of mascara will smudge and clump together if you apply liner after mascara. Applying mascara before liner also prevents you from being able to get as close to the lash line as possible. Remember - liner first, then two coats of mascara!