Buying them off the market, the odds of getting them in a pack are really low (I've gotten one ever). Basically you buy the guys from this week's team when you can get them for the best value, and that's when they are still in packs, but after people are already getting bored of them and ready for the next TOTW. That's usually sometime between Monday and Wednesday in the evenings US time the week after their released (so you should be looking at players from TOTW2 now) Don't buy stuff in the mornings US time because it is like 5-10% more expensive than it will be later in the day.
Anyway, pick an IF guy and look him up on FUTbin.com to see his price trend. If he's already trending upward, it is time to pick him up (in the late afternoon/evening) for the lowest price you can. You can usually pick a player up on an open bid relatively quickly for 90-95% of their lowest Buy it now listing. Don't fret too much about paying a few hundred more than your target value, you are buying at a relative low point in that player's cycle. Now you will hold him for 3-4 weeks as his price rises due to supply and command. The only reason to sell him before 3 weeks time is if he goes up rapidly in price due to price fixing or if you are afraid he will get a second in form card (usually they try to wait at least a few weeks between IFs for the same player, so unless he does something amazing like score 6 goals you don't have to worry about this).
I like to buy players that either fit nicely in hybrid squads (Argentinians or Brazilians in popular leagues, for example), players that have puber enticing stats, players that have a position change on their IF card, or good players in popular leagues who are going for near discard value (123 x their overall). If you pick them up for near discard value you literally can't lose on them. You can expect to gain a minimum of 25-50% return on your investment in 2-3 weeks for these first few rounds of in forms. As the year goes on, you can expect a steady 25% return after 4 weeks. What I like to do is invest in several each week, and after a month or so it creates a cycle of "maturing" players who are ready to sell so I can re-invest the coins in the next TOTW. This also keeps the game fresh as I like to build squads around the players I pick up.
So here are a few examples of players I'd recommend from Week 2:
Gignac - Good striker in good league going for around 10k (just over discard value). Build a team around him and enjoy playing with him for a few weeks while his value increases to 15-20k
Papy Mison Djilobodji - Beast of a CB with awesome stats in Ligue1 with potential African hybrid possibilies. Pubers will love his size/strength combo and I'm sure he'll get some positive reviews. He's also available for just over discard value (about 10k). He'll fit in that same Ligue1 team you build for Gignac and you can have fun bossing pubers around and I'd almost guarantee he'll end up well over 20k due to his size/strenght combo
FAT RONNY - He's probably too expensive for most of you, but this is the eventual goal. s a Brazilian silver in-form and they are always popular. His price is still fluctuating a little, but if you can grab him for under 70k (75k is current lowest BIN) then you'll probably have a great deal. In addition to being the always popular Brazilian silver, he plays in the Bundesliga which is a good league for silver teams. The secret here is that while pubers might not fall in love with his 66 pace, he does have 99 shot power in this in-form card. With long shots feasible again, he'll be a popular player. I'd expect him to be worth over 100k in a few weeks.