Shabbos Chazon, August 13, we daven Mincha at 5:25 p.m. The early Mincha allows time to return home for an appropriate pre-fast Seudah Shelishis. No classic pre-Tisha B'Av rules (e.g., eating on the floor, eggs, ashes et al) apply to this meal. The meal may include any foods, including meat and wine. Finish eating before sunset (8:23), when eating becomes prohibited. Other aspects of Tisha B'Av (low chair, non-leather shoes et al) are not applicable until later in the evening, when it is considered true halachic "night"
Motza'ei Shabbos is at 9:13. Wait until 9:13 and say Baruch ha-mavdil bain kodesh le-chol before doing work or making any preparations for Motza’ei Shabbos.
Our shul delays Maariv (followed by Eichah) until 9:30 to allow people to drive to shul after Shabbos.
If you begin to walk to shul for Maariv before Motza’ei Shabbos (9:13), then wear your Shabbos clothes and shoes. If that is what you plan to do, bring Tisha B'Av shoes to shul before Shabbos, (bringing them on Shabbos for Motza’ei Shabbos use is forbidden) so that you can slip into them right after the sheliach tzibbur says the Borchu of Motza’ei Shabbos Maariv. Those who leave their homes after 9:13 and say Baruch ha-mavdil bain kodesh le-chol may switch to Tisha B'Av shoes at home, although it better to wear proper shoes until after we begin Maariv.
We do not say a Motzaei Shabbos Havdalah. The aish beracha is said, on its own, on Motzaei Shabbos. You can say this aish beracha at home after having first said Baruch ha-mavdil bain kodesh le-chol, or may listen to it when it is said in shul.
The Motza’ei Tisha B’Av Havdalah is said without fire (done the previous night) or besamim. We may even use grape juice or wine for this Motza’ei Tisha B'Av Havdalah because Havdalah is a mitzva.
Ill people, who are not fasting, should use chamar medina (beer) rather than grape juice/wine for Havdalah on Motzaei Shabbos; coffee or tea may also be used, in which case cool the coffee/tea, so that it can be drunk within the short time span required by halachah. Although the ill person says Havdalah and the aish beracha on Tisha B'Av, he omits the introductory Hinei passage and the besamim.
May the Beis ha-Mikdash be rebuilt speedily in our days.
SA, OC, 552, 10
Rema, OC, 552, 10
As per Shemiras Shabbos ke'Hilchasah, 62, footnote 88
SA, OC, 556
Mishnah Berurah, 556, 3, although see Arukh ha'Shulchan, 556, 2
See Mikra'ei Kodesh, Pesach, 2, 47