The general rule in baseball and softball when it comes to running to first is you don't slide into first base. There are several reasons for this. The main reason is, that it is slower than if you run through the bag, despite what Harold Reynolds believes.
There is one exception to the rule. A high throw that takes the first baseman off of the bag. In this case, you can slide to avoid a possible tag.
As Erskine College's Baylee Browning demonstrates, you never slide headfirst on a ground ball to the pitcher. Because if you do, you might just scorpion the shit out of yourself, via Busted Coverage:
Reason #76 you don't slide at 1B (unless the throw is high and up the line to avoid the tag). #Ouch #Softball pic.twitter.com/DNZ9nhKiZk— Matt Lisle (@CoachLisle) February 23, 2017