Good question Retro, a few things come to mind. As others have pointed out - thinking in terms of success and failure can be a hindrance in itself. On the other hand I find it useful to try to be objective at the end of the meditation session and ask "how did it go? how much happiness, peace, freedom, etc. (or lack thereof)? why?" In this way I learn what are the causes that lead to the hindrance arising and what are the causes that lead to the enlightenment factors.
Also I highly agree that Dana and Metta are supportive to meditation practice and this is in concord with the Suttas:
Monks, for one whose awareness-release through good will is cultivated, developed, pursued, handed the reins and taken as a basis, given a grounding, steadied, consolidated, and well-undertaken, eleven benefits can be expected. Which eleven?
"One sleeps easily, wakes easily, dreams no evil dreams. One is dear to human beings, dear to non-human beings. The devas protect one. Neither fire, poison, nor weapons can touch one. One's mind gains concentration quickly. One's complexion is bright. One dies unconfused and — if penetrating no higher — is headed for the Brahma worlds.
- "Metta (Mettanisamsa) Sutta: Good Will" (AN 11.16), translated from the Pali by Thanissaro Bhikkhu. Access to Insight, June 7, 2009, http://www.accesstoinsight.org/tipitaka/an/an11/an11.016.than.html
"Having given this, not seeking his own profit, not with a mind attached [to the reward], not seeking to store up for himself, nor [with the thought], 'I'll enjoy this after death,'
" — but with the thought, 'This is an ornament for the mind, a support for the mind' — on the break-up of the body, after death, he reappears in the company of Brahma's Retinue. Then, having exhausted that action, that power, that status, that sovereignty, he is a non-returner. He does not come back to this world.
"This, Sariputta, is the cause, this is the reason, why a person gives a gift of a certain sort and it does not bear great fruit or great benefit, whereas another person gives a gift of the same sort and it bears great fruit and great benefit."
- "Dana Sutta: Giving" (AN 7.49), translated from the Pali by Thanissaro Bhikkhu. Access to Insight, June 7, 2009, http://www.accesstoinsight.org/tipitaka/an/an07/an07.049.than.html
It turns out I don't really have much to add that other people haven't stated already, but I find it encouraging to know that other people here practice in a similar way to me.