Obviously, I haven't been putting the ideas in to practice properly, or else I wouldn't keep losing so badly.

It doesn't help that a lot of my opponents' attacks (such as the one on my group in the top center-right) don't look like anything I saw in the book.

I'm sure A&D somewhere says not to touch opponent's stones when attacking . On the other hand such move can be seen quite often in similar situations. How about e.g. J17 instead? In this case it is not so easy for b to get a base; thus he will need to run in the center (and I think your 'iron pillar' in the corner would not easily die, even after the "tenuki"(?)). I'm not sure at all but would appreciate if anyone could give a qualified comment on this position.
I would have played that more or less automatically on F18. It makes the b group tendencially weaker, while your corner becomes big and almost totally invulnerable. If b replies G17 that would be a perfect result for w. If he plays ko you would have many ko threats with respect to the not yet fully settled black side areals.
In that constellation you have almost always the option to enter into 3/3 (R17). Either your 3/3 invasion connects to O17 or you have to abandon at least one of O17/L16 but live in the corner, thereby reducing b's upper right moyo and maybe even creating a weakish b group around there. Your move does almost nothing, if b would reply at the corner, e.g. Q18 (instead of his rather "thank-you" move) you essentially end up with three stones floating in nowhere.

First of all, this game is perhaps not the best for practising attack and defence, as there's not much attacking and defending going on with middlegame fights or weak groups, but nevertheless I'll try to make a few comments with that focus (and as always I'll repeat my advice to cheer up and not be so gloomy in your play, though I can appreciate real-life may get in the way of that).

- move 12: you are right that extending to the right is probably better. I'd prefer f17 over g17 so that it's not so easy for black to take the corner (he still could, but it would be cramped and gote rather than roomy and sente). The iron pillar protects the corner even more (and more pressure on the approach stone) but leaves the top side more open for invasion.

- move 14: your move is good, but if you want the top side to be yours you owe another move there, like g17 (but that's a bit slow). Now that black defended his c14 stone with c11, your corner got a bit weaker in that you can't attack c14 well, though you can still lean on it to get out with a move like d14. Notice that in terms of connectivity your top left and top right groups are quite far apart (compare with had you played f/g17).

- move 20: your move is good. Take a liberty. r9 sucks. s8 is nothing to worry about: even if black manages to connect he will damage the other side and have a low, weak shape.

- move 21: indeed. So let's think about attack and defence a bit here. Black c14-c11 is strong and even has d8 to help (so squeezing at c9 not effective). How about the white corner? It has some eyespace in the corner, but not a lot: for example imagine black slides to d18 and white answers at c18, d17 c17 then black b15 and answer at b16, that's an L group in gote, which is very dead (an L group in sente is dead). If black gets e15 you are loosely sealed in (but can cut and fight). So you don't want to be scrambling for a miserable corner life, but get out to the centre to keep yourself safe. How about black f17? It wants to extend to j17 to make a base, which is a key point to undermine l16 too (with l18 slide next). It can also slide to d18 to make a little eyespace and reduce yours a bit, and jump to the centre with f15 (or e15 to seal you) to run away. A stone with 3 ways to go is a pretty safe invasion, so you're not going to kill this stone, it's a legitimate invasion. So what to do? Well the first move I want to play is h17: to pincer black's invader (reduce eyespace) and make a nice territory/base for your top group. However this doesn't help you corner, so we need to consider if that would get in danger. Could black seal at e15? If you answered that by just living in the corner that sucks and means h17 wasn't an attack, so you'd need to cut and fight, which requires hard reading I'm too lazy to do now. If black jumped to f15 then you can come out nicely at d14. You could also thing about d14, but maybe black would ignore that to play j17, and then you could c13. Or he might hane because if you extend to e14 he doesn't need to defend the cut thanks to c11 and then j17. So maybe d14 then hane then you h17 pincer as that exchange helps a bit against the e15 seal.

- move 22: e17 is worse than your move, so well done for not playing it! The idea of getting out to the centre is a good one, BUT: f17 is weaker than c14 and remember the idea that touching stones makes them get stronger. So if you want to come out with an attachment it should be d14 (don't mind making a strong stone stronger) not f16. As schwipp says this is in A&D.

- move 25: black's big mistake, should e17.

- move 26: yes good move now. good shape

- move 27: and even worse move for black

- move 28: time for another attack and defence strength of groups analysis. Your corner is safe now and out to the centre; if black f18 you might want to answer but it's a bit wimpy. Black's group is out and has some sort of eyeshape but f18 atari would ruin a lot (he should ignore not connect). Your top right group didn't get any stronger since some time ago, and black's invasion now separates it from the corner, it got weaker. So you should either help this group or attack black's group. Your move does neither. Also note c14/c11/d8 si still strong and your move doesn't threaten it. So f18 instead is a good idea. Another good idea would be k17: this makes eyespace for your group and takes it away from black's, a wonderful move that is both attack and defence. Not sure which I prefer.

- move 30: is rather painful, but ok. Other idea: o15 as this defends in a way which has some future aim for r17.

- move 34: should hane. black can't cut or you capture the 2 stones, shouldn't be hard to read. This failure to hane meant your shape got worse (and black's better).

- move 36: there are other more efficient and eye-rich ways to defend like n14 or o14. Compare all this result to had you played at k17 not f13. You had a chance to make a base (and take black's).

EOC

is a place where you don't have to take gote.

is very passive. It's true that your group is not settled, but neither is black's stone! Even if you just play O10 before playing the move you've chosen, you'll have gained a foothold in the center with the white group, which will make black's group a little weaker and white's top center-right group slightly stronger.

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Occupy Babel!

I didn't think you could invade the corner at with the Black stone at R14 that close. I thought it had to be a point further away.

The standard invasion into that enclosure leads to ko: http://senseis.xmp.net/?4463Enclosure33Invasion

The above page assumes there are no white supporting stones. I think you can get unconditional life with the stone at O17.

I've put that position into a few variations. If there are any flaws (which is very likely the case...) I would appreciate corrections:

Uberdude is not suggesting an immediate invasion, but leaving it as a threat.

Moi, I would think about the jump attachment at Q-17 for move 30, with the aim of making immediate sabaki.

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The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

I presume you mean the sequence Q17, R17, R16?

After W Q-17, B R-17, both W R-18 and W P-16 should be considered. Not easy to read out, I am afraid.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

I have read this book 5 times and this is still my feeling.