In my book Breaking the Game, I discuss how to find the best play when faced with a set of candidates. This same decision making process also applies to Words with Friends, and is applied in the following positions. See if you can find the best strategic play in the following positions!
Puzzle 1:
Rack: 
Choices: KILIM 6b (26), VIAL k1 (20), VAIL k1 (20), KIVA g1 (31)
VIAL is better than VAIL. VAIL is easier to parallel than VIAL, meaning that your K setup is more likely to be blocked by your opponent, since you will not be making a parallel play with the IKS leave.
KIVA is better than KILIM because of the extra 5 points and roughly equivalent leave. While the K in the TWS alley looks scary, it’s actually somewhat difficult to use and will usually only net your opponent around 30 points.
I prefer VIAL to KIVA. The K setup is worth the 14 point sacrifice since it is quite difficult to score on this board without the setup. The ASV leave is unlikely to score 35 or more points next turn. In addition, the K hook can be preserved for next turn if you draw a high scoring play elsewhere.
Puzzle 2:
Rack: 
Choices: PROMOtES 10b (61), cOMPOSER 10b (61), IMPOSERs j8 (75), StOMPER 11f (68)
PROMOtES is better than cOMPOSER. cOMPOSER allows a lucrative scoring spot using the TL/TW combination that is much harder to use than PROMOtES.
STOMPER, IMPOSERs, and PROMOtES are all more difficult to compare, since the higher scoring plays are worse positionally. Because of the lack of scoring options after PROMOtES, I find it slightly preferable, however, if either of the bingos scored a few more points, they would become more attractive options.
Puzzle 3:
Rack: 
Choices: TERRAPIn 2e (55), RETRIM 4a (30), fIRETRAP 2c (57), fIRETRAP c1 (47)
TERRAPIn is a more attractive play than fIRETRAP 2c. TERRAPIn scores two less points but leaves much less for your opponent, since they cannot put a high scoring tile on a TW square. In addition, TERRAPIn opens two distinct TW squares: one for your opponent, and one for you.
TERRAPIn is also better than fIRETRAP c1, since it scores 8 more points. The only benefit for c1 is that it doesn’t open an additional quadrant, but with the additional 8 points and short term defense, TERRAPIn outweighs these factors. If need be, you can sacrifice points to close quadrants later, but this concept is less important in WWF than Scrabble.
I prefer RETRIM over TERRAPIn. It scores 25 points less, but it keeps the valuable blank and opens far less in terms of scoring spots. Individually these factors are less important than the points, but combined these factors outweigh the 25 points.
Puzzle 4:
Rack: 
Choices: QUOTE 6j (30), COME 9f (29), OUTCOME h4 (28)
COME is superior to OUTCOME. While it keeps an inferior ETU leave, the U is more useful than usual because of the open Q, and COME leaves far less open for your opponent than OUTCOME.
I prefer COME to QUOTE. QUOTE leaves a D/R/S hook in the TW/TL lane which can be extremely lucrative. Although the leave is clearly superior, that huge opening is not worth the difference in leave.
Puzzle 5:
Rack: 
Choices: FID k5 (25), GID k5 (24), GELID k3 (30), IF k6 (29), FETID k4 (31)
GELID is better than FETID. The extra point of FETID and equal leave is overruled by the ease of forming parallel plays to the right of FETID, especially those parallel plays that hit the TW square.
Likewise, GID is better than FID. While the leaves are nearly equal, it is much easier to parallel FID than GID.
I prefer GID to IF. While IF scores 5 more points, it keeps a worse leave and gives your opponent more high scoring options, especially if they have an S in their rack.
I also prefer GID to GELID. While GELID scores 6 more, the TW opening and slightly worse leave make GELID slightly inferior.