(for fashion shoots) bulldog clips are a great alternative to safety pins* which can sometimes leave holes in clothing. get them at any store that carries business supplies and get them in various sizes. use bigger ones for bulkier clothes and for lightweight clothing uses the smaller clips.
additional tip: for really delicate clothing use paper towel in between the clothes and the clip to help prevent any accidental snags.
*if you insist on using safety pins use caution. make sure to position your hand with the garment so in case of a slip, you hit yourself with the pin and never the model. use extra caution when working with kids. also, never, ever use straight pins! those are dangerous and become a hazard to everyone who handles the clothing if the stylist forgets to remove them after a shoot.