I have created a tutorial to do this. Take a look here: Produce PCA for 1000 Genomes Phase III in VCF format
If your genotype is in vcf format, you can convert it to plink format then use the --pca function from PLINK.
If you have large number of samples (which shouldn't be the case if you are using 1000G), then you can consider flashPCA
Note: If you are directly converting the vcf to plink format, make sure you handled the multi-allelic SNPs and you might also need to manually edit the bim file such that there isn't any duplicated SNP id