When I was a kid I used to have handstand competitions with my sisters and my Dad (who was really good), anyways that put some motivation into gaining proficiency. Also when I wrestled in high school we would to tumbling before practice, like sommersaults and what not, but one of the things that we would do is try to walk across the wrestling mat on our hands. Believe after you start practicing it everyday you begin to get better. I can prob hold it for a good 45 sec to 1 min now, but I haven't timed myself in a while. Just keep at it and like someone said earlier something usually seems to click and you just feel like you have better balance. After that it's just how long you can usually concentrate on good form.