Platinum
First thing I did recently was catch a few Pokemon. In honey trees I found a male Aipom and a female Combee, both of which I caught. I also caught a Gastly in the Eterna Forest, and Bronzor in Route 211. Sadly, I had to take Shadowfax, my Ponyta, off my team, because I already had a Fire-type (a Monferno) on it--which was a shame because his Flame Wheel was the strongest attack any of my teammates had.
I replaced Shadowfax with the Bronzor I just caught, which I nicknamed Ferrum (after an old Latin word for iron). I primarily put it there because of its high defenses and the fact that it's psychic-type and knows Confuse Ray, one of my favourite attacks.
I also added a Buizel I caught before to my team, naming it Weasley. So far my team consists of:
Imp (female Monferno)
Electra (female Luxio)
Erika (female Budew)
Vul (male Staravia)
Weasley (male Buizel)
Ferrum (Bronzor)
All I did afterward was train my team a bit. Ferrum just learned Extrasensory last night, a huge improvement over Confusion. Erika's been holding a Soothe Bell ever since I got it, but she's at level 20 now and still hasn't evolved... But that hardly matters, as she won't be of much use in the battle with Gardenia.
Speaking of the battle with Gardenia, I think for this battle I'll temporarily put Shadowfax back on my team, since he's Fire-type--and I'll have Weasley sit it out. After all, I bet Gardenia's Pokemon could easily KO even a level 20 Buizel.
Diamond
Training, training, training... always the same. Well, not quite. Some of my Pokemon have grown quite a few levels in the past few days, most notably my Froslass, who grew ten levels. She's now at level 40. Also, I took her to the Move Relearner, where she learned Confuse Ray and Ominous Wind.
I spent most of this morning training Arthur and Guinevere, my Gallade/Gardevoir couple. A couple of days ago they learned Psycho Cut and Psychic, respectively, an improvement over Confusion (especially on Arthur's part, because his Special Attack is lower). First they trained in Route 211, then Route 218--although there, Arthur had a problem with the Mr. Mime, and Guinevere had a problem with the Floatzel. For a while, Guinevere did a lot better in her training than Arthur did, because Arthur had problems with the Graveler on Route 211 and in Mt. Coronet (he fainted once from Selfdestruct) and couldn't do as much damage with Shadow Ball. But after I took Arthur to the Move Relearner to learn Leaf Blade, he did a lot better. He's catching up to Guinevere level-wise; he's at level 38 and she's at 39.
(In case you're wondering about the Shadow Ball, both of them know it because I bred them for it. Their father--a Drifblim--knew Shadow Ball.)