I will try to explain how to create a proper tactics here. Tactics that (hopefully) won't result in your team getting beat 20-0 in your first game. It is more of a "practical guide" than a how-to, so if you don't know how to go about creating tactics, then you should be better of reading this first. If you already know how to create tactics, then here are a few pointers on what to watch out for so you won't make a mess out of the game.
Although it's perfectly OK to experiment with formations, it can backfire and backfire good! If you go too far with experimenting, you can cause your players to get totally lost and confused on the pitch and that will result in you getting beat,... bad! With common formation, we are thinking something along the lines of 4-4-2, 4-3-3, 5-4-1, 4-5-1, 5-3-2, 3-5-2 or some other well known formation used in football nowadays. Of course it's ok to experiment with more defensive or offensive variations (like 4-4-2 diamond with 1 attacking midfielder and 1 defensive midfielder), but 1-1-8 (for example) formation just won't work in this game, it's not allowed and will result in your team playing with bot 4-4-2 random formation.
Well we all know that midfield is the "heart" of the team out there on the pitch, but saying that, having better midfield alone just won't guarantee you success here. While it will probably give you more possession, you still need good defenders to link up or start the play and, of course, a striker or two upfront to score them goals. You also need to be carefull on style of play because if you choose to play with many guys in the midfield, the chance is that long balls just won't work as the players will mostly be near each other on the pitch. So think about your tactics and what you are trying to achieve.
And I just cannot stress this enough! Sending bunch of guys that can barely stand on their feet from exhaustion alone will certainly result in you bringing home a few(if not more) goals in your net! Check the player's condition (on the profile screen) before you put him in your first 11 for the next match! Remember players lose condition points after each match and after each hard/very hard training session and while they can still play at 80 they will walk around the pitch like zombies if their condition level falls below 50 (and I don't really need to say what happens if you play the guys with even lesser condition level do I?).
You should check the weather forecast for the match day before you decide on tactics for the match. For example, if the match will be played during the rain storm on wet pitch, the short/direct passing probably won't lead to a fluent creative play.
While it's good to save one substitution just in case if someone gets injured out there, it is still recommended to bring a few fresh legs to the pitch at one time in second half. While you'll be giving a substituted player a rest, the player coming on to the pitch will be full of energy and will probably wreak havoc amongst the (now already tired) opponent's players.
There are lots of cases where you can surprise and totally outplay your opponent just by selecting the right tactics! For example, if the opponent has a weak left side (a young inexperienced wingers/full backs for example), then you can exploit that by placing a good and quick right winger on the pitch and instruct the players to try build an attack over the right side of the pitch. If your opponent has a couple of good defenders that are not too good in heading, then you can use a couple of good wingers with instruction to build up play over left+right wing, that will(hopefuly) result in more high crosses into opponent's penalty area. If you have a striker there that can score with his head... There are many such situations and all are pretty logical, you just need to think about the opponent and what tactics he/she will use on a match day.
I've seen numerous mistakes when people only fielded
one (1) classic defender and thought that if they field 2 or 3 defensive midfielders that their goal
will be safe. That cannot be farther from the truth! Use defenders for defending your goal! At least
1 central defender is needed (if supported by at least 2 full/wing backs), and use 3 central defenders
if you are playing without full/wing backs as playing with 2 central defenders(even if you add a
defensive midfielder) proved to be too risky and it's not worth it (can quickly result in couple of
conceded goals). As with "use common formation" tip, the same applies here. Use a real-world football
for "tactical templates", and you don't see many teams playing with one defender and 8 forwards nowadays
do you?
I hope the tips above will help you in creating a succesfull tactic that will lead
your team to the top of the table. For more tactical tips (including a short description of skills
needed for each position), you can check the tactical FAQ