Well that surely must depend on what you have to hand, and how stringent you want to gag yourself.
Over The Mouth Gag
The over the mouth method - in the old 50's film and TV series, a damsel was always tied with one of the over the mouth gags.
This is much more effective if you use mouth packing IE a wad of rolled cloth or handkerchief (please use a clean one) put into the mouth. The picture is by FOOTFETISH.COM
The Cleave Gag.
This is usually a strip of cloth or a scarf tied behind the neck that is forced between the teeth.
To improve on this, again, you can use mouth packing IE a wad of rolled cloth or handkerchief. Another way maybe to tie a thick not in the middle of the cloth.
I am sometimes gagged with a long piece of cloth that is wrapped around my head twice and tied at the front, so that the knot forms the packing.The picture is by INEXESSE.COM
A tape gag is a strip or two of very sticky electrical tape or duct tape. The English sometimes call it Gaffer Tape. Ladies if you are going to get all dolled up before your bondage, your makeup foundation may prevent the tape sticking and ruin your lipstick too. To make this an effective gag, again you can use mouth packing.
The Ball Gag.
This is a small wooden or latex ball with a piece of strap or string to fasten behind the neck. The ball is positioned behind the teeth then tied in place.This method forces the mouth stuffed wide open. As a result this can make you drool all over the place especially if your head is forced into a downward position.
The Ring Gag.
This is a metal ring usually covered in a latex or leather wrapping that is positioned behind the teeth. It is attached to a strap that is fastened behind the neck.
The Panel Gag
This gag is usually a ball gag with a leather covering forming an over the mouth
panel. The picture is by BDMAX.COM
The Bit Gag
The bit gag looks like a horses bit, IE made of metal or more usually a straight strip of hard rubber or latex, attached to a strap by rings, that can be fastened behind the neck. Picture by AFETISHPAGE.COM
The Harness Gag.
Harness gags can either be of a bit or ball nature. With more straps to tie it completely to the face, once it is on you wont be able to spit the ball or bit out. I know, I've tried one and couldn't. The picture is from BALLGAGGED.COM
The Rope Gag
This is a length of rope either knoted or not, put between the teeth. Here is Christina Carter from a HOGTIED.COM
Several other gags are inflatable or chopstick gags and there are even medical and dentist type gags to choose from.
Safety: the only safe gag is the ring gag as you can breath through it if you are choking or being sick. Nothing prevents the fluids passing out of your mouth. Inflatable gags can be inflated to much and choke. Mouth packing can be swallowed and cause choking. Please be aware some people may be allergic to Latex gags. In fact anything inserted into the mouth can potentially be dangerous, so please play safely .
Happy Bondage, Emma x