Speed · Plain-English answer
Connect to the nearest server with spare capacity, use the WireGuard protocol if your app offers it, and prefer a wired or strong Wi-Fi connection. Restarting the app and your router clears stuck sessions. If speeds are still poor, test several servers, because load varies more than most people expect.
Server choice comes first. A server one country away will almost always beat one an ocean away, and within a country a lightly loaded server beats a popular one. Most apps show load or ping estimates, so use them rather than picking the top of the list.
Protocol comes second. WireGuard moves data with less overhead and recovers from network changes faster than older protocols, so switch to it if your app offers a choice. Third, fix the local link: a laptop on weak Wi-Fi loses more speed to the wireless hop than to the VPN.
Measure your baseline with the VPN off at /tools/speed-test/, then repeat the test on two or three different servers. If every server loses roughly the same amount, the bottleneck is local, so look at Wi-Fi, the router or the device. If one server is dramatically worse, the problem is that server.
Also close background sync tools and downloads while testing, since cloud backups quietly consume upload capacity and make any VPN look slower than it is.
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