data mining (machine learning)
high dimensional data analysis
probability theory
statistics
graph theory
popular programming/analysis tools:
python, matlaab, r, java, perl (less popular), c++
most of the NGS software is written in c++, java and python.
Some p[ossible directions if you are interested in software development:
RNA-seq data analysis
ChIP-seq data analysis
data visualization tool
server-based data analysis pipeline
user-friendly GUI development --- for bench folks