I want to second this post...I often wouldn't have funds until a day after you guys bought in and I'd jump in too late (paying too much in the process) thinking I could just make a little less. I usually ended up missing out entirely or just barely getting my money back. It is totally worth your while to sit on your money until a prime opportunity arises. You may miss out on a good play, but there will be plenty more to make up for it...and if you lose that money jumping in late, you won't have any money to get into the good ones that suddenly pop up.
Patience is a virtue here.
Also, don't jump the gun assuming an STP is going to complete as you will find they often take a few attempts before they take off...which may make your entry cost twice what it could have been. Use the chart and await confirmation. You and your account will be glad you did.
“The two most important days in your life are the day you are born and the day you find out why.” —Mark Twain.