One thing I learned when applying was how remarkably different each school's application procedures were. For whatever reason, I assumed that these procedures would be largely the same; what a foolish mistake! Some schools required official transcripts while others did not. One school (GSU) would not accept official transcripts sent directly from the schools, requiring me to have transcripts sent to me for me to bundle and then send to GSU. UWM required letters of rec to be mailed by my professors. Some schools required me to mail my writing sample and statement of purpose. Some schools required that I send documents to both the philosophy department and the graduate school. One school (UMSL) had an incredibly short (150 words!) maximum word count for statements of purpose.
In short, don't be a dumb like me and assume that application procedures are homogenous.
Also, applying to grad school is very expensive. I applied to 9 schools (which is fairly low compared to others on here), and between application fees, GRE fees, and official transcript fees, I probably spent around $1,000, so save up!