On some of the chips, the pins will be angled so that they are too wide to fit into the sockets. The pins must be gently bent back into position.
If you are using the BeebMaster disc upgrade kit, beware as the 8271 pins are much firmer than those on the smaller ICs.
Once the pins are correctly aligned, place the chip in the socket and ensure that all the pins are resting just above the holes. Then apply even pressure across the whole microchip to secure the device in place.
If you are doing this for the first time, the crisp, cracking sound which makes you think the chip is crumbling to bits is quite normal so don't panic!
Double check that the chips are installed in the correct sockets and the right way round. Don't skip this stage in a rush to get playing Elite - you'll be Harmless forever if you get it wrong!!