i) there is only a small group of irregular verbs to learn
ii) They still have the same endings as the regular verbs so you only need to remember the stem
For example, if we take the verb “decir” (“to say” / “to tell”) which is irregular in the future tense verb, you can see that if you learn that the stem shortens from the full verb decir to dir and then you just add on the same set of endings as with any future tense verb:
The most common irregular verbs and their future tense stems to memorise are these ones:
You just add the future endings onto the end of each stem.
caber > cabr + future ending (to fit)
decir > dir + future ending (to say/tell)
hacer > har + future ending (to make/do)
poder > podr + future ending (to be able)
poner > pondr + future ending (to put)
querer > querr + future ending (to want)
saber > sabr + future ending (to know)
salir > saldr + future ending (to go out/leave)
tener > tendr + future ending (to have)
venir > vendr + future ending (to come)
There are more irregular verbs but for people just starting to learn Spanish, these are the main ones to start learning for everyday use.