Why do my bmx bike brakes suck?

[IanAF]

i have front and back u brakes and the front ones are new. they always really never worked well at all. i would have to squeeze it all the way to the grip. then i fooled with the adjusting barrel on the brake lever. now they are much easier to brake. i can get it to brake but it still doesnt stop fast enough? the pads slide on the rim kinda. anyway it doesnt brake quick enough and it is still hard to do tricks with my front brakes. i think it is the pads or the brakes are just cheap. help