Planner cost adjustments

Hi all,

Running some queries, I found that the planner often selects sequential scan instead of an index scan, even if the latter is way faster (one order of magnitude faster if I consider some tests I made by setting enable_seqscan = ON/OFF). How can I figure out what parameter I should adjust to get the planner select an appropriate plan that would better consider my DB setup?

I had a look at http://www.postgresql.org/docs/9.3/static/runtime-config-query.html but at this point it is too much information for me;-)  Any rules of thumb, recipes I could use to select which parameters I should look at first?

Daniel