How to focus when recording video using a DSLR? I'm looking for advice on how to adjust focus effectively when using a DSLR to record video.  I find it difficult to judge focus on the small LCD screen on the back of the camera when focusing manually, and the auto-focus feature is not very useful during recording.

I am aware that it's possible to attach external monitors which help by having larger screen or focus peeking.  Other than expensive external accessories, what techniques can one use to achieve the best results in various situations?

I am not looking to get serious about video making.  I'm simply trying to find out what I can do with the video feature of a DSLR I got primarily for still photos, and focusing has been one of the major pain points so far.   I was successful only when pre-setting focus, and not adjusting it during recording.
Other than what you mentioned, the only other alternative is to use a third party firmware that highlights the points of highest contrast.  This gives you a better idea of what is focused on by highlighting the edges that are sharp in the LCD.  MagicLantern offers this for most Canon cameras.  I don't know if third party firmware for other DSLR makes has similar features or not.