Tenses

I was doing

long action in the past, usaually at same time as past simple

when, while, as long as

I had been doing

action taking place before a certain time in the past, sometimes interchangeable with past perfect simple.

for, since, the whole day, all day

I have done

began in past, still here. effect.

alread, ever, just, never, not yet, so far, till now, up to now

will be doing

arrangements, plans, in progress, action that is sure to happen in the near future

in one year, next week, tomorrow

will have been doing

duration, not finished

for..., the last couple of hours, all day long

will do

spontaneous decisions, prediction, request, offer

in a year, next, tomorrow, probably, perhaps, Conditional I, I think

will have done

result, finished, action that will be finished at a certain time in the future

by monday, in a week

I did

completed action

yesterday, 2 minutes ago, in 1990, the other day

I had done

story in past which happened in the past

already, just, never, not yet, once, until that day, Conditional III
 

going to do

strong predicion, personal interests & plans

I do

Timetables, schedules.

words to help: always, never, normally, often, seldom, sometimes, usually

I am doing

Social & business arrangements

at the moment, just, just now, listen! look!, now, right now

I have been doing

putting emphasis on duration of course, finished action that influenced the present

all day, for 4 years, since 1993, how long? the whole week