There is no big golden rule to success in Battrick. You need to keep experimenting to find out whats best for your team. What works for another may not work for yours.
Thats what everyone uses friendlies for. They are the best way to experiment with your team, shuffle the order round etc because if you lose the game it doesnt really matter. Of course in the PC Battrick tournament, there are very high levels of competitiveness, so most people use their 1st squad.
I would recommend what Zorax said, especially reading the rules twice because they are so useful.
A couple of other tips I have picked up from various places (mainly here):
1) Forget the Youth Academy. It is much better to save up for really good players. Of course, still have a go at promoting Academy players (otherwise known as youth pulls) on Saturdays, just in case you get a great player).
2) Each player (may) have a hidden preference for which spot in the batting order they like. This is something you can only discover by shuffling them around in friendlies.
Okay, thats enough. Best of Luck!