install IconBeFast&BlazeWCP from Aminet or install new graphics.library from Aminet too.
Use MagicWB icons: they save up ram and don't require extra cpu power. Directories with many newicons/glowicons will take much longer time to load even if newicons author claims to have written very fast routines. SwazInfo or something like that may be useful to have an improved "info" tool that allows you to update icons using drag'n'drop. Some tool to lock first 8 colours may be handy
Install MUI and ClassAct, as specially the first one is required by a lot of apps. Directory Opus 4.x is a must.
Don't forget SnoopDos to discover why some programs fail and what libraries do they require.
KingCon is a must if you are going to use Amiga Shell as it allows auto-completion and other goodies.
Update picture.datatype, you can take it from picasso96. Perhaps you need updated datatypes.library, I can't remember
Install AK-Datatypes. These are fast and free.
Use ToolsDaemon because Amidock and other docks don't integrate well with AmigaOS and just bloat the system. ToolsDaemon is the best since sliced bread :-D
For games you should install "iGame" as it makes game loading much more comfortable than browsing directories from WB and will even show you a nice preview if you want. It requires some extra libraries and MUI MCCs available on
http://www.aminet.netDownload PPaint from Aminet to prepare your backgrounds... it's better you resize and dither your background pictures to match WB resolution. Keep various versions in your HD in case you want to update them. Anyway keep in mind that using small tiled backgrounds is much more effective with your config.
Install some app to bring windows to front double-clicking them. MultiCX for example allows that although there are other options (with the system a commodity called "clicktofront" is included but it just uses a single click like Windows, something very annoying for Amiga users. Avoid multi-patches like MultiCX or MCP.
Install "Meridian" from guido mersmann if you use a mouse with a 3rd button or a wheel. Assign gestures to switch screens and enjoy :-)
Install CBM Installer if you don't have it :-D
Install SmartFileSystem and use it for your work partition. If you have created a single big unique partition forget it and create at least 2 partitions... we amigans love partitions and keep in mind that it's better to lose a partition than lose the complete HD.
Make a backup of your RDB. It could save your life.
Download fat95 and some pcmcia drivers to use compactflash/sd adapters as it's a comfortable way to install new data. Check out if your ram card as a jumper to set 4MB instead of 8MB and prepare a cable to be able to switch when the computer power off. This will allow you to have access to PCMCIA as 95% of A1200 ram cards with 8MB block pcmcia access (I never saw the remaining 5% with my own eyes but I have read in amiga.resource.cx that certain models are compatible, perhaps it's a mistake and if it does then add it to the 95%)
Download some Demos from Amiga Demoscene Archive like Nexus7 and enjoy your A1200 :-D