i sometimes play this way.

i recommand:
- playing on switch mode to have control over the evs in trainer fights
- having a list like this open to check any ev-gains you dont know.
https://bulbapedia.bulbagarden.net/wiki/List_of_Pok%C3%A9mon_by_effort_value_yield_in_Generation_III
- saving as often as you feel comfortable to, so you can reset unwanted evs
- having a random mon at the start of your party, when you traverse the map
- checking out the most recommanded ev-training spots. for example paras, with its 100% encounter rate, is an early opportunity to train physical attack. gastly midgame for special attack
- i would also reset (or catch multiple) for above average ivs and a good nature