Ok, in my minimal experience with suturing vaginas and perineums, here is what I have learned If it's superficial and not bleeding, and it comes together nicely when the woman's legs are shut, then you probably do not need any suture in it.
A vaginal pocket (small little gap at the vaginal introitus) usually closes nicely with a figure of 8. Or two of them.
Find the apex in the vaginal laceration, and work your way outward. Use a locking stitch.
2-0 vicryl on a CT needle is my favorite suture material for vaginal lacerations.
3-0 chromic on an SH needle heals best for periurethral lacerations.
The transverse perineal muscle looks like a sausage when it's lacerated. (Make sure you match the lacerated ends of the sausage back together!)
Knot tying is harder to do with wet gloves.
Staunch the flow of lochia with a tagged sponge/lap, so you can view the area to be repaired.
Sometimes you need three hands to suture things back together.
Suturing the superficial perineal skin back together is very rewarding. Everything looks so pretty again!
When in doubt about the depth of the laceration (a possible 3rd or 4th), call in the attending MD. After all, they are highly skilled surgeons. The same thought apply to a "what the heck?" laceration where you can't make heads or tails of what goes where. It bears repeating: OBs are great at surgery, thus, they are amazing at sewing things back together.