Battery terminals are the first place to look. Battery to chassis ground is the next. Sometimes these cables corrode inside the insulation where you can't see it. Try cleaninig up the connections and if that doesn't help, replace the battery to starter positive cable. The negative (ground) cable can also corrode. You can also try using a heavy jumper cable to directly power the starter, but be careful.
Don't be gormless; get some gorm!