you have to stay tight. whatever direction you are falling you have to put pressure on the opposite side of your hand. it depends what direction you are falling. you can also walk on your hands because sometimes that helps you stay up longer.
If you want to make your hand stand straight and standing up for a while , use the wall, kick up against the wall and when u feel like your going to fall use the wall to keep your self up. Once you get comfortable with standing on your hands then soon enough u will be able to do a hand stand for a longer period of time.
JUST do THIS every DAY for a FEW minutes...( or as long as you'd like )
i still havent mastered the hand stand but in wresting we have to walk on our hands nd i found out if u take it slow ull be a master n no time plus i cant go straight back on a back bend i have to do maytricks its funny lol