Simple graphs are a very good way to look for overall patterns in the data. They can help identify trends as well as deficiencies. Common graphing methods are:

Histograms
Time series
Comparisons
Pie charts

Comparative Statistics:
Comparative statistics are used to assess the strengths of the relationships among different datasets (e.g., streamflow and sediment concentration, paired watersheds, BACI.)

Some common techniques are:

Correlations
Regressions
Student t-tests
Analysis of variance (ANOVA)

It is important to know the difference between a correlation and a regression relationship. Both describe the strength of relationship between two quantitative variables. Correlation (r) does not distinguish between explanatory and response variables. Regressions (r2) distinguish between dependent (response) and independent (explanatory) variables.