Maximum number of students start preparing seriously from the month of October.As only 4 months left I think swallowing standard textbooks along with a job is not going to be optimal.I think following steps will be very usefull
1.watch all the video lectures of GATE LECTURES BY ************ ****** from youtube.It will take 1 month to complete only the youtube videos but its very useful along with simultaneous practice from gateoverflow.Make notes of each new concept and problems you come across.If u don't do simultaneous practc then u wont feel confident.
2.Watch chapterwise videoes from NPTEL which ************ did not give on youtube(You can go for full course provided by him but that's your choice).
3.Cyclic revision of each concepts and problems.Gateoverflow has biggest collection of every possible problem that may be asked in gate.
4.Try to focus on graph theory and math.You will get lots of resources in internet.they are very scoring.From this point as you will be beginning from 0 don't run for 100% syllabus,select 70-80% syllabus and do it with perfection.
5.Make use of internet as much as possible.there is no shortcut to gate except clever use of resources availbl in internet.
6.Stay motivated always.Even last yr some of my seniors cracked gate with only 2-3 months of preparation.Maximum dedication and practc for next 4 months is needed,here motivation will play a big role,u wont feel tired.
7.Before attempting gate,try to attempt at least 4-5 mock tests after completion and revision.Its really needed for time management and improvement of thught process.
All the best!hope this will help.