With this patch you can focus on any of the currently open windows on the current tagset with just one key combination

dwm.c

@@ -228,6 +228,7 @@ static void tagmon(const Arg *arg);
 static void tile(Monitor *m);
 static void togglebar(const Arg *arg);
 static void togglefloating(const Arg *arg);
+static void focusbynum(const Arg *arg);
 static void toggletag(const Arg *arg);
 static void toggleview(const Arg *arg);
 static void togglewin(const Arg *arg);
@@ -2043,6 +2044,19 @@ togglefloating(const Arg *arg)
 	arrange(selmon);
 }
 
+void
+focusbynum(const Arg *arg)
+{
+	int i;
+	Client *c;
+
+	i = 0;
+	c = nexttiled(selmon->clients);
+
+	for (; c && i < arg->i; c = nexttiled(c->next), i++);
+	focus(c);
+}
+
 void
 toggletag(const Arg *arg)
 {