I use a degreaser such as 5l Swarfega Oil & Grease Remover or No-No sense heavy duty degreaser from Screwfix, toothbrush, small paintbrush, nailbrush etc.
Small parts that are extra cruddy I leave in a plastic tub filled with degreaser overnight.
Also gets your teeth super clean if you forget to rinse the toothbrush afterwards
Clean motorbike parts with petrol and wd40, cycle parts with wd40 but now use Fenwicks FS1 concentrate as i got a 5l bottle of it cheap. Very strong and will strip paint if not rinsed/washed off straight away if using neat :shock: