FastQC
A quality control analysis tool for high throughput sequencing data
...This should then direct you to where your data may have problems and allow you to take necessary steps to correct it before doing any further analysis.
FastQC is not tied to any specific type of sequencing technique, so it can be used to look at libraries of various experiment types (Genomic Sequencing, ChIP-Seq, RNA-Seq, BS-Seq etc etc).