I've been writing up a lot of battle reports lately so they're at the forefront of my thoughts, and when I saw this post on The Warhammer Forum I had the answer already. The poster asks what he can do to turn around a losing streak. This was my answer:
The best thing you can do to turn around a losing record is to write up battle reports of all your games just after you've played them. It can take a bit of time but it really does make you analyze your list, your opponent's list and the tactics you used during the game.
After each report write down three things you'd change about the game if you could; it could be bringing different guns to take on particular units, having more mobility, attacking on a narrow front instead of table wide or going second instead of first.
After a few games I guarantee you'll spot a trend that you'll be able to correct by either adjusting your tactics or tweaking your army list.
One of the good things about 5th edition, I think, is that there are now a number of ways to play the same army differently. The variety of different missions and deployment types plus the control you have over reserves means you can radically change your army play style without changing a single model in your list.
Of course it's nice to be able to do something with those battle reports when you've spent all that time writing them which is the reason I have my battle reports blog.
The latest game I've just added is the second at The Gauntlet Tournament. Check it out here.