you will pass out be for you get to 250
do your 50 and every day add one more push up soo see if that works ^_^
but don't let it end there w8 like 5 minuets or so and do some pull ups and push ups endurance is half the battle
go for a run maybe swim, jump rope and stretch
then start punching things maybe get a punching bag or some jerk you dont like (j/k)
all in all 300 push ups is a Nobel effort but that alone isn't enough to feed your body or maybe it is I don't know
good luck