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I'm a single digit kyu and recently find myself giving real handicaps (other than to complete beginners when introducing the game) for the first time. This has led to many losses. At one point I got up to a 5k Kiseido rank by taking a handicap from bots ranked 1k or so and winning, but giving handicap I lose often to weaker players (bot & human) so I'm down to 9k now.
Basically, I have no idea how to handle the white side at handicap. Search here has not turned up much on the topic. Has anyone got advice? Or links?
There are basically two ways to play a handicap:
The former strategy is more of a gamble and includes some psychological warfare. The latter is more "correct" but it needs more patience on your behalf. You can try both strategies and see which suits you best. If you are a good fighter, the former may suit you. If you are good at the endgame, the latter may be preferable.
Another advice may be to play moves which are technically and strategically sound but not very common. Those may unsettle an opponent who relies on set patterns. For example, opening at 10-10 is uncommon but not as bad as its rareness would suggest. Or an approach at 6-4 to a 4-4 corner stone, which isn't used very often and may fool your opponent into either the idea that you know some kind of secret or that you don't know what you're doing.
Seek territory and also thickness. Avoid helping Black settle (unless he is paying an arm and a leg to do so). This is because Black's main metric for finishing the game ahead is settling the board. Due to the handicap stones simplifying and filling in presumably means substantial amounts of black moyo are converted to points, while opportunities for White to survive and build disappear. If something like a white moyo ever is formed it will throw your opponent for a loop, for the same reasons you asked this question... Not only is this an unfamiliar quantity and spacing of white stones, the decision to ignore/reduce/invade demands counting and whole-board assessment skills. And Black rarely has the discipline to tenuki even after blatantly gote moves, which is not to say if you have unprotected big points/groups they will not eventually be bashed with a sledgehammer.
Patience is very important; one could argue that fully half or more handicap games will be won near the very end. It goes without saying that you should be very sharp and outplay your opponent both in fiddly little tactics and awareness (if sometimes powerless awareness) of what's next on the board. This is one of the joys of Go between different ranks - you can practice your life and death, and endgame skills, with some more blatant examples of urgent middle game points, in a simultaneously challenging and forgiving environment, allowing different focus. Invasion/reduction in particular.
Dieter's answer is spot on, though the approaches stated are maybe just ways you might play to improve focus on understanding particular conditions. Basically, a flexible approach is the only correct approach, but it doesn't aid in understanding ideals like influence, territory, security. You can go back and forth in how you try to think of these and which ones are dominant many times in the course of a Go career.
Example: when someone is just about to push past the 9-stone handicap, I'll try attaching to handicap stones, hane and other contact plays, crazy often style. It's something different and indeed reasonable locally and on some counts but bad against a savvy Black who can exact a fair exchange and settle.
If you don't know where to begin, start from your most impeccable approach to even games and see if you can transition this through games with no komi, 2 stones, 3 stones, and so on. Once you can, the laundry list of advice becomes, "just play normal."
@crazy often style: While it may be the best way to win a handicap game, what is the best way to win a handicap game that remains a teaching game? The result of crazy often play are quite often intimidated handicap players that adapt by playing defensively - which is far too often sufficient to carry home a 9 stone handicap, but not exactly a way to improvement for them. Now, to encourage them to play better, it would be wonderful if I could win more games if they play badly. Usually amongst amateurs it is the other way round, the correct way to play leads to more losses until the player toughens up (in local fighting, better reading) significantly, thus pushing players to a deplorable way to play handicap games.
Well basically, I play simply and more cautiously when playing 9-stone games against players who need 9 or more stones, and as they are on the cusp of consistently winning, desperation tactics are instructional. This is an important point to add to the advice though - honesty is a necessary quality for the white player to cultivate. Indeed in real life games, the meta game communication by the sound of each move, position of eyes, etc. is substantial and mistakes in this are to be avoided as much as game mistakes.