IGCSE Stoichiometry seems like a nightmare to most students. There are many reasons to it. Some of the common ones being that the student may have not expected such  calculations into chemistry and hence might be unwilling to concentrate on whats being taught in class. To add to this , it might be the teacher who might have not really dealt with the concept really well, not giving enough examples. Whatever the  reason, we need to know that the problem needs to be addressed and the student must perform. So keeping this in mind, i would make some few suggestions here. Break the IGCSE Stoichiometry into different topics such as : Percentage yield/ Limiting and excess reagents/Molar gas volume etc. Once you have made the  list, try pulling your school or any reference book that you have and read through one subtopic at a time. Next attempt to understand the solved example if any and try to rework it with understanding. Next is refer online to videos  for the same subtopic and try to solve a different variety of sums as the video teaches you. Next take the past paper questions, beginning with multiple choice ones then going to the extended theory. Understand the  way marks are allotted in the marking scheme. We  ( https://www.smartexamresources.com )have some really in-depth bifurcated IGCSE topic wise past papers  ( sure you wont find this quality  classification elsewhere)for  Chemistry/Math/Physics/Biology/Economics. You may try  the IGCSEEconomics questions given below . Having done that the mastery of IGCSE Stoichiometry should not seem tough. And if you feel  that its a Herculian task, then watch the video on Complete Stoichiometry -By Smart Exam Resources on you tube and also shared below, it will take just 35 minutes to master it for sure. Good luck  and may you all do really well always.