Factor 1. You must have "enough" backlinks for these pages (only Google knows for sure how much will be enough, but I was testing this on dozens of sites and if you build really lots of quality backlinks to 2 URLs - it will work)
Factor 2. Give some time for Google to "digest" the info (once again, only Google knows for sure how much time is enough to digest all the backlinks to your URLs, but my tests show that within 4-6 weeks of nice link building you will see the results)