Mine have an after school routine that includes homework and they don't get any 'free time' until their homework has been done. I type up a quick homework timetable and stick it on the back of the kitchen door and in their school diaries, so they know in advance what homework they need to do each evening.
They come home, get changed out of their uniforms and come downstairs and for a quick drink and snack. Then its straight into homework and when its done they have the rest of the evening free to do as they please.
Ds1 (9, year 5) has ASD and needs me to sit with him through all his homework, ds2 (7, year 3) just goes to fetch his on his own, gets started and asks me if he needs my help. I also test him on spellings, time tables and number bonds the evening before his school test. If either of them has a strop and refuses to do their homework, they know that they won't be allowed on their nintendo Dsi's until its been completed.
I intermittently reward them with half an hour playing their favourite game on my laptop, for being particularly good or working extra hard and I actually find this is far more motivating than a regular reward, although last year I bought a job lot of Pokemon stickers off ebay. They got to choose one sticker for each piece of homework they completed and stuck them into a little notebook, so they built up a little pokemon character collection as the year went on - they both loved that.
We have a rule that homework is done the day its brought home, unless they are at a club or after school activity, then it gets done the next day. We don't do homework at weekends, partly because I feel they need a complete break from school over the weekend and partly because I know I'm likely to meet more resistance if I schedule it for then.
We have been through periods in the past where we have had lots of arguments and refusals, but I made sure that I was consistent and stuck with the rules. I threatened to write to their teachers a couple of times, telling them that they have refused to do the work - and that's usually a remarkably effective motivator.
The start of a new school year is always a little bit bumpy while they get used to the new homework timetable etc, but we are into the swing of it already this year and so far they've been really good.