Black/White to Move and Win
Here is a good exercise I lifted from a recent book I read. I've started doing this with the The Week in Chess files I download every week, located at The Week in Chess Downloads .
Load up the TWIC pgn file into your favorite database. Fire up a decent chess engine. Go through GM games (both sides) that are a win result (i.e., skip draws), starting about 10 moves or so back from the end. Note the victor - White or Black - that is who you will be playing. Find the point in the game where your chess engine shows the victor being up > 2.00. (This can be adjusted to a lower or higher value depending on how you want to set up your practice: +/- of 1.00 would more difficult to win, and higher values would be easier to win.)
Here is an example.
(26) Agdestein,S (2565) - Bacrot,E (2710) [E73]
FIDE World Cup (1), 2013
1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Be2 0-0 6.Bg5 Na6 7.Qd2 c6 8.Nf3 e5 9.0-0 exd4 10.Nxd4 Nc5 11.f3 Nfxe4 12.Nxe4 Nxe4 13.fxe4 Bxd4+ 14.Qxd4 Qxg5 15.Qxd6 Rd8 16.Qa3 Rd2 17.Rfe1 Be6 18.Qc3 Rad8 19.c5 R8d4 20.b3 Rxe4 21.Bf3 Red4 22.Re3 Bd5 23.Re8+ ... 0-1
After White made the move 23.Re8+, the position evaluation went to -+(-2.59) on my machine using the Fritz 8 Engine, from under -+2.00), so this, for our purposes, is the "tipping point". At this point you want to pick up the game as Black and attempt to win it against the computer. Don't look at the how the GM won, and don't be shy - let the computer play at a strength that is at least a class or two above your own. If you fail to win the game, try again.
This is terrific practice for your technique in winning won positions. And, what's great is it matters not what the opening was or any other aspects of the game. you are just trying to practice winning won positions.
If you are like me, you don't win all your won games! This attempts to improve your skills in this part of your game, and you get a good cross section of current events in chess, not to mention it is a whole lot of fun!