If one has prepared and inspected oneself properly before immersion, there is no need to look for problems afterwards. However, if a woman is concerned that her tevilah may not have been valid, she should not hesitate to ask a question (see Finding a Problem after Immersion for guidelines.)
According to many authorities, one should not shower again at the mikveh after immersion. This ensures that one doesn't imagine that the shower, rather than the mikveh, made one tehorah.
When a woman comes home from the mikveh, she should tell her husband verbally that she immersed.